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chem 0330 - midterm 1 Flashcards

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1
Q

what are the solubility rules

A
  1. most nitrate salts are soluble
  2. most salts of sodium, potassium, and ammonium are soluble
  3. most chloride salts are soluble. exceptions: silver chloride, lead chloride, mercury chloride
  4. most sulfate salts are soluble. exceptions: barium sulfate, lead sulfate, calcium sulfate
  5. most hydroxide salts are only slightly soluble. exceptions: sodium hydroxide, potassium hydroxide, and calcium hydroxide (marginally soluble)
  6. most sulfide, carbonate, and phosphate salts are only slightly soluble
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2
Q

what is the term for a reaction in which the equilibrium position favors the products such that the reaction appears to have gone to completion

A

it lies far to the right

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3
Q

what is the term for a reaction in which the equilibrium position favors the reactants such that the reaction barely appears to have happened?

A

it lies far the left

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4
Q

what are the two possible reasons why the concentrations of the reactants and products of a given reaction remain unchanged when mixed

A
  1. the system is at equilibrium

2. the fwd and reverse reactions are so slow that the system moves toward equilibrium at an undetectable rate

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5
Q

what is the law of mass action

A

K = [C][D]/{A][B], where C and D are the products and A and B are the reactants, K is the equilibrium constant, and each species is raised to the power of its coefficient in the balanced chemical equation

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6
Q

what is the equilibrium expression for a reaction written in reverse

A

the reciprocal of that for the original equation

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7
Q

what is the equilibrium expression for a reaction in which the balanced equation is multiplied by a factor of n

A

the original expression raised to the nth power

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8
Q

in which cases must corrections for non-ideal behavior be applied to the law of mass action

A
  1. concentrated aqueous solutions

2. gasses at high pressures

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9
Q

is the equilibrium constant constant for a reaction at the same temperature regardless of the amounts of gasses that are mixed together initially? are the individual equilibrium concentrations always the same?

A

yes, ; for a reaction at a given temp, there are many equilibrium positions but only one value for K; the specific equilibrium position adopted by a system depends on the initial concentrations, but K does not

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10
Q

in what other way can the equilibrium expression be written

A

in terms of the equilibrium partial pressures of the gases; Kp represents an equilibrium constant in terms of partial pressures

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11
Q

what is the relationship between K and Kp

A

Kp = K(RT)^change in n, where change in n is the sum of the coefficients of the gaseous products minus the sum of the coefficients of the gaseous reactants

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12
Q

what are homogenous equilibria

A

systems in which all reactants and products are in the same phase

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13
Q

what are heterogenous equilibria

A

equilibria that involve more than one phase

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14
Q

how do we treat pure solids or liquids involved in a chemical reaction when creating the equilibrium expression

A

if pure solids or pure liquids are involved in a chemical reaction, their concentrations are not included in the expression for the reaction

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15
Q

what does knowing the equilibrium constant for a reaction allow us to predict

A
  • the tendency of a reaction to occur (albeit not the speed of the reaction)
  • whether a given set of concentrations represents an equilibrium condition
  • the equilibrium position that will be achieved from a given set of initial concentrations
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16
Q

what indicates the inherent tendency for a reaction to occur

A

the magnitude of the equilibrium constant

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17
Q

what does a value of K much larger than 1 mean

A

at equilibrium, the reaction system will consist mostly of products; the equilibrium lies to the right; reactions with very large equilibrium constants go essentially to completion

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18
Q

what does a very small value of K mean

A

the system at equilibrium will consist mostly of reactants; the equilibrium position is far to the left; the reaction does not occur to any significant extent

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19
Q

are the size of K and the time required to reach equilibrium directly related

A

no, the time required to achieve equilibrium depends on the reaction rate, the size of K is determined by factors such as the difference in energy between products and reactants

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20
Q

how do we know if a mixture is at equilibrium and, if it isn’t, in which direction the system will shift to reach equilibrium

A
  • if the concentration of one of the reactants or products is zero, the system will shift in the direction that produces the missing component
  • if all of the initial concentrations are not zero, we use the reaction quotient, Q
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21
Q

how is the reaction quotient obtained

A

by applying the law of mass action, but using initial concentrations instead of equilibrium concentrations

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22
Q

to determine in which direction a system will shift to reach equilibrium, we compare the values of Q and K

A
  • If Q = K, the system is at equilibrium; no shift will occur
  • if Q > K, the ratio of initial concentrations of products to initial concentrations of reactants is too large. For the system to reach equilibrium, a net change of products to reactants must occur. The system shifts to the left, consuming products and forming reactants until equilibrium is achieved
  • if Q < K, the ratio of initial concentrations of products to initial concentrations of reactants is too small. The system must shift to the right, consuming reactants and forming products to attain equilibrium
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23
Q

how can we make the math simpler when doing equilibrium calculations

A

if K is super small, we can can eliminate it

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24
Q

how can we quantitatively predict the effects of changes in concentration, pressure, and temperature on a system at equilibrium

A

by using Le Châtelier’s principle

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25
Q

what is Le Châtelier’s principle

A

it states that if a change in conditions (a stress) is imposed on a system at equilibrium, the equilibrium will shift in a direction that tends to reduce the change in conditions

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26
Q

what is the effect of a change in concentration on a system at equilibrium

A

if a gaseous reactant or product is added to a system at equilibrium, the system will shift away from the added component. If a gaseous reactant or product is removed, the system will shift toward the removed component. in short, the system shifts in the direction that compensates for the imposed change in conditions

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27
Q

what is the effect of the addition of an inert gas on a system at equilibrium

A

the total pressure increases but has no effect on the concentrations or partial pressures of the reactants or products (assuming ideal gas behavior); thus, the system remains at the original equilibrium position

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28
Q

what is the effect of a change in volume of the container of a system at equilibrium

A

the concentrations (and thus the partial pressures) of both reactants and products are changed. For systems involving gaseous components, when the volume of the container is reduced, the system responds by reducing its own volume. It does this by reducing the total number of gaseous mlcs in the system. so, shifts to side of reaction with less moles. Vice versa is also true

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29
Q

does the K value change with temperature

A

YES

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30
Q

what is the effect of adding heat (increasing temp) to an exothermic system (energy is a product) at equilibrium

A

the reaction shifts left, increasing the concentrations of the products, decreasing the value of K

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31
Q

what is the effect of adding heat (increasing temp) to an endothermic system (energy is a reactant) at equilibrium

A

the reaction shifts right, increasing the concentrations of the reactants, increasing the value of K

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32
Q

what is an acid

A

a proton donor

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33
Q

what is a base

A

a proton acceptor

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34
Q

what is a conjugate base

A

what remains of the original acid molecule after a proton is lost

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35
Q

what is a conjugate acid

A

the product formed when a proton is transferred to a base

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36
Q

what is Ka

A

the acid dissociation constant; only used to represent a reaction in which a proton is removed from HA to form the conjugate base A-

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37
Q

where does the equilibrium lie for a strong acid

A

far to the right; almost all original HA is dissociated at equilibrium

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38
Q

what are the strong acids

A
  • HCl - hydrochloric acid
  • HNO3 - nitric acid
  • HBr - Hydrobromic acid
  • H2SO4 - sulfuric acid
  • HI - hydroiodic acid
  • HClO4 - perchloric acid
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39
Q

what type of acid yields a weak conjugate base

A

a strong acid

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40
Q

where does the equilibrium lie for a weak acid

A

far to the left; most of the acid originally placed in solution is still present as HA at equilibrium

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41
Q

what type of acid yields a strong conjugate base

A

a weak acid

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42
Q

is Ka large or small for a strong acid

A

large

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43
Q

is Ka large or small for a weak acid

A

small

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44
Q

how does the strength of water as a base compare to the strength of the conjugate base of a strong acid

A

water is stronger

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45
Q

how does the strength of water as a base compare to the strength of the conjugate base of a weak acid

A

water is weaker

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46
Q

what does Kw represent

A

the dissociation constant that refers to the auto-ionization of water; for any aqueous solution, no matter what it contains, [H+][OH-] must always equal Kw

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47
Q

what is the value of Kw (at 25 degrees C)

A

1 x 10 ^-14

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48
Q

describe a solution in which [H+] = [OH-]

A

neutral, both concentrations = 1x10^-7

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49
Q

describe a solution in which [H+] > [OH-]

A

acidic

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50
Q

describe a solution in which [H+] < [OH-]

A

basic

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51
Q

what is pH equal to

A

-log[H+]

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52
Q

what is pOH equal to

A

-log[OH-]

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53
Q

what is pK equal to

A

-logK

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54
Q

how do you do sig figs for logs

A

the number of decimal places in the log is equal to the number of sig figs in the original number

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55
Q

what is pH + pOH always equal to (for any aqueous solution at 25 degrees celsius)

A

14

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56
Q

what should always be the first step in solving acid-base problems

A

writing the major species present in the solution

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57
Q

how should you calculate the pH of a strong acid solution

A

when calculating the pH of a strong acid solution, decide which species is the main contributor of H+ ions (the acid or the water) and calculate the pH using the concentration of H+ that comes from that species

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58
Q

how should you calculate the pH of a weak acid solution

A

decide which species is the main contributor of H+ ions. it is then an equilibrium situation, so we need to make an ICE chart for the reaction of the species that is the main contributor of the H+. solve for x in the normal way. find the value that applies to the [H+] and then find the pH

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59
Q

how should you calculate the pH of a mixture of weak acids

A

decide which species is the main contributor of H+ (this will be the species with the biggest K). once you find this, you need only find the pH of that part and that will constitute the pH of the whole solution. to find the pH, make an ICE chart using the reaction of that species, find x, find value of H+, find pH.

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60
Q

what is the percent dissociation of a strong acid

A

assumed to be 100%

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61
Q

what is the percent dissociation of a weak acid

A

amount dissociated/initial concentration x 100

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62
Q

for a weak acid, how are the percent dissociation and the concentration of the acid related

A

the percent dissociation increases as the acid becomes more dilute

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63
Q

what are the strong bases

A

sodium hydroxide, potassium hydroxide, group 1 hydroxides, group two hydroxides are strong but not very soluble

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64
Q

how should you calculate the pH of a strong base

A

determine the major OH- contributor. assume 100% dissociation and calculating pOH. then find pH by subtracting pOH from 14.

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65
Q

what is Kb

A

the base dissociation constant; always refers to the reaction of a base with water to form the conjugate acid and the hydroxide ion

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66
Q

how should you calculate the pH of a weak base

A

find the main effector of pH, find an equation for the Kb of that species using the balanced reaction, solve for x, find [OH-] find pOH, find pH

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67
Q

what are polyprotic acids

A

acids that can furnish more than one proton per molecule

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68
Q

how do polyprotic acids dissociate

A

in a stepwise manner, one proton at a time

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69
Q

when deciding whether a solution is acidic, neutral, or basic, Ka > Kb means it is

A

acidic

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70
Q

when deciding whether a solution is acidic, neutral, or basic, Ka = Kb means it is

A

neutral

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71
Q

when deciding whether a solution is acidic, neutral, or basic, Ka < Kb means it is

A

basic

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72
Q

how can you calculate the fractions of the various species present in a solution of a polyprotic acid

A

the fraction of each species is the concentration of that species divided by the total concentrations of all species

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73
Q

how do the Ka1, Ka2, … Kaj values for a typical weak polyprotic acid compare

A

Ka1 > Ka2 > … > Kaj

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74
Q

how can you calculate the pH of a solution of a polyprotic acid

A

typically, only the first dissociation step is important in determining the pH, so just treat that reaction as a typical weak acid problem

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75
Q

what is special about sulfuric acid

A

it is a strong acid in its first dissociation step and a weak acid in its second step; usually only step 1 matters, but sometimes depending on concentration (if dilute enough, less than 1.0M) we need to consider step 2

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76
Q

how do salts that consist of the cations of strong bases and the anions of strong acids affect [H+] when dissolved in water

A

they don’t; thus, aqueous solutions of salts like KCl, NaCL, NaNO3, and KNO3 are neutral

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77
Q

how do alkali metal ions affect pH

A

they don’t

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78
Q

how are Ka and Kb related for any weak acid and its conjugate base?

A

Ka x Kb = Kw

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79
Q

for any salt whose cation has neutral properties and whose anion is the conjugate base of a weak acid, will the aqueous solution be acidic, basic, or neutral?

A

basic

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80
Q

a salt whose cation is the conjugate acid of a weak base produces an [acidic/basic/neutral] solution?

A

acidic

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81
Q

what is the significance of a highly charged metal ion in a salt

A

this salt will produce an acidic solution; Al+3 is a highly charged metal ion, and hen hydrated it is Al(H20)6 positive 3 charge, which dissociates into Al(OH)(H2O)5 positive 2 + H+, which makes the solution acidic

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82
Q

what is energy

A

the capacity to do work or to produce heat

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83
Q

what is the law of conservation of energy

A

energy can be converted from one form to another but can be neither created nor destroyed; the energy of the universe is constant

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84
Q

what are the two types of energy

A

Potential and kinetic

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85
Q

what is potential energy

A

energy due to position or composition

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86
Q

what is kinetic energy

A

energy due to the motion of the object and depends on the object’s mass and velocity

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87
Q

what is temperature

A

a property that reflects the random motions of the particles in a particular substance

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88
Q

what is heat

A

involves the transfer of energy between two objects due to a temperature difference

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89
Q

what is work

A

force acting over a distance

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90
Q

what are the two ways to transfer energy

A

through work and through heat

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91
Q

is energy a state or a path function

A

state

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92
Q

is work a state or a path function

A

path

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93
Q

is heat a state or a path function

A

path

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94
Q

what is a state function

A

refers to a property of the system that depends only on its present state; does not depend on how the system arrived at the present state

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95
Q

what is the system

A

the part of the universe on which we wish to focus attention

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96
Q

what are the surroundings

A

everything else in the universe thats not the system

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97
Q

what is an exothermic reaction

A

when a reaction results in the evolution of heat; energy flows out of the system

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98
Q

what is an endothermic reaction

A

reactions that absorb energy from the surroundings; heat flows into a system

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99
Q

where does the energy, released as heat, come from in an exothermic reaction?

A

the heat flow into the surroundings results from a lowering of the potential energy of the reaction system; in any exothermic reaction, the PE stored in the chemical bonds is being converted to KE via heat

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100
Q

what does the change in PE stored in the bonds of the product compared to the bonds of the reactants represent

A

the difference between the energy required to break the bonds in the reactants and the energy released when the bonds in the products are formed.

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101
Q

in an exothermic process, how do the bonds of the products compare to the bonds of the reactants

A

the bonds of the products are stronger (on average); more energy is released in forming the new bonds in the products than is consumed in breaking the bonds in the reactants

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102
Q

does making a bond absorb or release energy

A

release

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103
Q

does breaking a bond absorb or release energy

A

absorb

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104
Q

in an endothermic reaction, what is the energy that flows into the system (as heat) used to do

A

to increase the PE of the system

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105
Q

in an exothermic reaction, do the products or the reactants have a higher PE

A

reactants

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106
Q

in an endothermic reaction, do the products or the reactants have a higher PE

A

products

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107
Q

in an endothermic reaction, how do the bonds of the products compare to the bonds of the reactants

A

the bonds of the products are weaker (on average)

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108
Q

what is the first law of thermodynamics

A

the law of conservation of energy; the energy of the universe is constant

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109
Q

how can the internal energy of a system be changed

A

by a flow of work, heat, or both

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110
Q

what two parts do thermodynamic quantities always consist of

A

a number and a sign

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111
Q

what does the sign in a thermodynamic quantity reflect

A

the system’s point of view; if energy flows into the system, q is positive, indicating that the system’s energy is increasing, and vice versa

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112
Q

if the system does work on the surroundings, what sign does w get

A

negative

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113
Q

if the surroundings do work on the system, what sign does w get

A

positive

114
Q

why do work and P(change in V) have opposite signs

A

b/c when the gas expands (changeV is positive), work flows into the surroundings (w is negative), and vice versa

115
Q

what is the work accompanying a change in volume of a gas often called

A

PV work

116
Q

in dealing with PV work, what does the P refer to

A

external pressure; the pressure that causes a compression or that resists an expansion

117
Q

what does the variable q stand for

A

heat

118
Q

what is the variable for enthalpy

A

H

119
Q

is enthalpy a state or a path function

A

a state function

120
Q

a process carried out at constant pressure only allows what kind of work to take place

A

PV work

121
Q

for a process carried out at constant pressure (where the only work allowed is that from a volume change) how are enthalpy and heat related

A

change in enthalpy of the system = the energy flow as heat; for a reaction at constant P, the flow of heat is a measure of the change in enthalpy for the system

122
Q

if the products of a reaction have greater enthalpy than the reactants, is change in enthalpy positive or negative

A

positive; heat is absorbed, rxn is endothermic

123
Q

if change in enthalpy is positive (at constant P), is the reaction exothermic or endothermic

A

endothermic

124
Q

if the reactants of a reaction have greater enthalpy than the products, is change in enthalpy positive or negative

A

negative; heat is released, rxn is exothermic

125
Q

if change in enthalpy is negative (at constant P), is the reaction exothermic or endothermic

A

exothermic

126
Q

what is the only way to change the kinetic energy of an ideal gas

A

change its temperature

127
Q

what is the molar heat capacity of a substance

A

the energy required to raise the temp of 1 mole of that substance by 1 kelvin

128
Q

if an ideal gas is heated in a rigid container, is there PV work? why or why not?

A

no, because there is no change in volume, so change in v = 0

129
Q

if an ideal gas is heated in a rigid container (no change in volume, no PV work), where does all the energy that flows into the gas used for?

A

to increase the translational energies of the gas molecules

130
Q

what is the variable for molar heat capacity

A

C

131
Q

what is Cv (molar heat capacity of an ideal gas at a constant volume)

A

(3/2)R; thus, (3/2)R is the amount of “heat” required to change the temp of 1 mole of gas by 1 K at a constant volume

132
Q

what is different about heating a gas at constant pressure vs constant volume

A

at constant volume, no PV work occurs, so all the energy going in increases the KE of the gas molecules; in contrast, at constant pressure, PV work does occur, so energy is supplied to both the KE of the gas and to provide the work the gas does as it expands

133
Q

what is Cp (the heat required to increase the temp of 1 mole of gas by 1 K at constant P)

A

(3/2)R + R = (5/2)R
or
Cv + R = Cp

134
Q

why do polyatomic gases have a Cv greater than (3/2)R

A

bc some of the energy added via heat flow is “stored” in motions that don’t directly raise the temp of the gas (like rotational and vibrational motions)

135
Q

is the larger Cv for polyatomic gases related to whether or not the gas is behaving ideally

A

no

136
Q

what is the equation for when a gas is heated at constant volume

A

change in E = Cv(change in T)

137
Q

what is the equation for when a gas is heated at constant pressure

A

“heat” required = nCv(change in T)

138
Q

what is the equation for change in enthalpy, regardless of any conditions on pressure or volume

A

change in enthalpy = nCp(change in T)

139
Q

what is the only thing that the enthalpy of an ideal gas depends on

A

Temperature

140
Q

what equation is used to calculate the heat flow of an ideal gas

A

q = mC(change in T), where Cv or Cp is used, depending on the conditions

141
Q

at constant volume, what is heat flow equal to

A

change in E

142
Q

at constant pressure, what is heat flow equal to

A

change in H

143
Q

what is a calorimeter

A

a device used to determined the heat associated with a chemical reaction

144
Q

what is calorimetry

A

the science of measuring heat

145
Q

what is the heat capacity of a substance

A

C = heat absorbed/increase in temp

146
Q

what is specific heat capacity

A

the energy required to raise the temp of 1g a substance by 1 degree celsius

147
Q

what is molar heat capacity

A

the energy required to raise the temp of 1 mole of a substance by 1 degree celsius

148
Q

what is constant pressure calorimetry used for

A

determining the changes in enthalpy occurring in solution b/c under conditions of constant pressure the change in enthalpy = the heat

149
Q

if two reactants at the same temp are mixed and the resulting solution gets warmer, is the reaction exothermic or endothermic

A

exothermic

150
Q

if two reactants at the same temp are mixed and the resulting solution gets cooler, is the reaction exothermic or endothermic

A

endothermic

151
Q

is any work done in constant pressure calorimetry (reactions in solution)

A

no b/c change in volume is 0

152
Q

in constant pressure calorimetry, what 3 quantities are equal

A

change in E, change in H, and q

153
Q

for a reaction involving gases at constant pressure, are change in E and change in H always equal?

A

no

154
Q

for an ideal gas, when is the only time that work occurs

A

when volume changes

155
Q

is work done in calorimetry experiments performed at constant volume

A

no

156
Q

what is Hess’s Law

A

b/c enthalpy is a state function, in going from a particular set of reactants to a particular set of products, the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps

157
Q

what are two important things to remember when using hess’s law

A
  1. if a reaction is reversed, the sign of changeH is also reversed
  2. if coefficients in a balanced reaction are multiplied by an integer, changeH must also be multiplied by that integer
158
Q

what is the standard enthalpy of formation of a compound

A

the change in enthalpy that that accompanies the formation of 1 mole of a compound from its elements with all substances in their standard states

159
Q

what is the standard state for a substance

A

a precisely defined reference state

160
Q

what symbol indicates that the corresponding process has been carried out under standard conditions

A

the superscript 0

161
Q

what is the standard state for a gas

A

a pressure of exactly 1 atm

162
Q

what is the standard state for a substance present in a solution

A

a concentration of exactly 1 M at an applied pressure of 1 atm

163
Q

what is the standard state for a pure substance in a condensed state (liquid or solid)

A

the pure liquid or solid

164
Q

what is the standard state for an element

A

the form in which the element exists (is most stable) under conditions of 1 atm and the temp of interest (usually 25 degrees C)

165
Q

how can the enthalpy change for a given reaction be calculated

A

by subtracting the enthalpies of formation of the reactants from the enthalpies of formation of the products

166
Q

are elements in their standard states included in the changeHreaction calculations

A

no; change in standard enthalpy of formation for an element in its standard state is 0

167
Q

what does it mean for a process to be spontaneous

A

if it occurs without outside intervention

168
Q

what is the driving force of all spontaneous processes

A

an increase in entropy

169
Q

what does the probability of occurrence of a particular arrangement (state) depend on

A

the number of ways (microstates) in which

170
Q

what is the formula to determine the number of microstates for a given arrangement

A

N!/(L!R!), where N = total number of molecules, L = number of molecules in the left bulb, R = number of molecules in the right bulb

171
Q

rank solid, liquid, and gas in order from least to most entropy

A

Solid < liquid < gas

172
Q

what is an isothermal process

A

one in which the temperatures of the system and the surroundings remain constant at all times

173
Q

for any isothermal process involving an ideal gas, what is the change in energy equal to

A

0

174
Q

for any isothermal process involving an ideal gas, what is heat (q) equal to

A

-w (negative work)

175
Q

what is a free expansion

A

one in which no work is done in expanding the volume of a gas

176
Q

what is work equal to in a free expansion

A

0

177
Q

when the expansion of a gas is carried out in an infinite number of steps, what is the relationship between the external pressure and the pressure produced by the gas

A

they are essentially equal

178
Q

what is a process carried out so that the system is always at equilibrium called

A

a reversible process

179
Q

as the number of steps in an isothermal gas expansion increases, what happens to the work

A

it also increases

180
Q

what is the maximum work that a given amount of gas can perform in going from V1 to V2 at constant temperature

A

it occurs in the reversible expansion; wmax = wrev = nRT(ln(V2/V1))

181
Q

as the number of steps in the isothermal compression of a gas increases, what happens to the work required to compress the gas

A

it also decreases

182
Q

what is the significance of expanding/compressing a gas reversibly (in an infinite number of steps)

A

Only when the expansion and compression are both done reversibly (in an infinite number of steps) is the universe the same after the cyclic process; only for the reversible processes is the heat absorbed during expansion equal to the heat released curing compression; in all processes carried out using a finite number of steps, more heat is released into the surroundings than is absorbed in the comparable expansion

183
Q

what happens to work in any finite-step, cyclic expansion-compression process

A

work is always converted to heat

184
Q

what is the relationship between the input of work and the output of work in an irreversible cyclic process

A

more work must be input to the system than the system produces

185
Q

are all real processes reversible or irreversible

A

irreversible

186
Q

when does the maximum work obtainable from the gas occur

A

when the expansion is carried our reversibly

187
Q

what is a reversible cyclic process

A

one in which both the system and the surroundings are returned exactly to their original conditions

188
Q

what is an irreversible process

A

one in which even when the system is cycled and thus returned to its original state, the surroundings are changed in a permanent way

189
Q

what is the only condition in which a reversible process can occur

A

equilibrium

190
Q

what is the second law of thermodynamics

A

in any spontaneous process, there is always an increase in the entropy of the universe; the entropy of the universe is increasing

191
Q

how can we predict whether a given process will be spontaneous

A

we must know the sign of changeSuniverse; if positive, the process is spontaneous in the direction written; if negative, the process is spontaneous in the opposite direction; if 0, process has no tendency to occur, indicating that the system is at equilibrium

192
Q

in an endothermic process, what is the direction of heat flow

A

out of the surroundings and into the system

193
Q

in an exothermic process, what is the direction of heat flow

A

out of the system and into the surroundings

194
Q

does an exothermic process in the system increase or decrease the entropy of the surroundings

A

increase

195
Q

does an endothermic process in the system increase or decrease the entropy of the surroundings

A

decrease

196
Q

what does the sign of changeSsurroundings depend on

A

the direction of the heat flow

197
Q

what does the magnitude of changeSsurroundings depend on

A

the temperature; the transfer of a given quantity of energy as heat produces a much greater percentage change in the randomness of the surroundings at a low temp than it does at a high temp; thus, changeSsurroundings depends directly on the quantity of heat transferred and inversely on temperature; in other words the tendency for the system to lower its energy becomes a more important driving force at lower temperatures

198
Q

at constant pressure and temperature, changeSsurroundings is equal to what

A

-(changeH)/T

199
Q

what is free energy defined as

A

G, G = H - TS

200
Q

what is the equation for changeSuniverse as related to G at constant T and P

A

changeSuniverse = -(changeG)/T

201
Q

when will a process carried out at constant temp and pressure be spontaneous

A

only if changeG is negative

202
Q

a process at constant T and P is spontaneous in which direction

A

in which the free energy decreases

203
Q

how can entropy changes of the system in chemical reactions be predicted

A

by considering the changes in positional probability; in a reaction involving gaseous molecules, the change in positional probability is dominated by the relative numbers of molecules of gaseous reactants and products

204
Q

if the number of molecules of the gaseous products > the number of molecules of the gaseous reactants, what does this mean for changeS

A

changeS is positive for that reaction; vice versa is also true

205
Q

on a fundamental level, what does the change in enthalpy determine

A

whether a reaction is exothermic or endothermic at constant pressure

206
Q

on a fundamental leve, what does change in free energy determine

A

whether a process is spontaneous at constant temp and pressure

207
Q

what is the third law of thermodynamics

A

the entropy of a perfect crystal at 0 K is 0; a perfect crystal represents the lowest possible entropy

208
Q

does the entropy of a substance increase or decrease with temperature

A

increase

209
Q

which equation is used at the melting point or boiling point to account for the entropy change that accompanies the change of state

A

changeS = changeH/T

210
Q

what do standard entropy values represent

A

the increase in entropy that occurs when a substance is heated from 0K to 298K at 1atm

211
Q

how can the entropy change for a given chemical reaction be calculated

A

by taking the difference between the standard entropy values of the products and those of the reactants; number of moles of a given reactant or product must be taken into account

212
Q

how is molecular complexity related to standard entropy value

A

the more complex the molecule, the higher the standard entropy value

213
Q

what is the standard free energy change

A

changeG^o; the change in free energy that occurs if the reactants in their standard states are converted to the products in their standard states

214
Q

why is it useful to know changeG^o for a reaction

A

knowing changeG^o values for several reactions allows us to compare the relative tendency of these reactions to occur

215
Q

the more negative the value of changeG^o….

A

the further a reaction will go to the right to reach equilibrium

216
Q

does changeG^o tell us anything about the rate of reaction

A

no; it only tells us about its eventual equilibrium position

217
Q

is free energy a state or path function

A

state

218
Q

what is the standard free energy of formation of a substance

A

the change in free energy that accompanies the formation of 1 mole of that substance from its constituent elements with all reactants and products in their standard states

219
Q

what is the standard free energy of formation of an element in its standard state

A

0

220
Q

what do a negative large magnitude of changeG^o indicate

A

that the reaction is very favorable thermodynamically

221
Q

a reaction system at constant temp and pressure will proceed spontaneously in which direction

A

the direction that lowers its free energy

222
Q

why do reactions proceed until they reach equilibrium

A

b/c a reaction system at constant temp and pressure will proceed spontaneously in the direction that lowers its free energy

223
Q

what is the lowest free energy value available to a particular reaction system

A

the equilibrium position

224
Q

why does the free energy of a reaction system change as the reaction proceeds

A

b/c free energy depends on the pressure of a gas (or on the concentration of species in solution)

225
Q

for an ideal gas is enthalpy pressure-dependent

A

no

226
Q

for an ideal gas, is entropy pressure-dependent

A

yes b/c it depends on volume

227
Q

at a given temp for a mole of ideal gas, what gives the gas greater entropy, large volume or small volume?

A

large volume; S(large volume) > S(small volume)

228
Q

at a given temp for a mole of ideal gas, what gives the gas greater entropy, high pressure or low pressure?

A

low pressure; S(low pressure) > S(high pressure)

229
Q

if a reaction system has a negative changeG, does that mean that the system will proceed to completion

A

no, it will go to equilibrium, because the equilibrium position is the lowest possible free energy available to it

230
Q

if a phase change reaction has a negative changeG, will that phase change go to completion

A

yes, because the end of the phase change has the lowest free energy; there is no intermediate substance with lower free energy

231
Q

where does the equilibrium point for a reaction system occur

A

at the lowest value of free energy available to the reaction system

232
Q

why is the point of minimum free energy for a reaction system the equilibrium point

A

for a reactant, A, turning into a product B, as A turns to B, its G decreases because its pressure decreases. Conversely, the G of B increases because its pressure increases. The reaction proceeds in this way as long as the total free energy of the system decreases, which is as long as Gb is less than Ga. Once A and B reach the same pressure, Ga = Gb. At this pressure, changeG for the reaction is 0. Thus, the system has reached minimum free energy and there is now longer any driving force to change A to B or B to A, so the system remains here and the pressures of A and B remain constant

233
Q

what does it mean when changeG^o equals zero for a particular reaction

A

The free energies of the reactants and products are equal when all components are in the standard states; the system is at equilibrium when the pressures of all reactants and products are 1 atm, meaning that K = 1

234
Q

what does it mean when changeG^o < 0

A

changeG^o would be negative, which means that G^o of the products < G^o of the reactants. At 1 atm, this system is not at equilibrium. The system will shift right to reach equilibrium. K >1

235
Q

what does it mean when changeG^o > 0

A

ChangeG^o would be positive, which means that G^o reactants < G^o products. At 1atm, this system is not at equilibrium. It will shift left to reach equilibrium. K < 1.

236
Q

if changeG^o = 0, what is K

A

1

237
Q

if changeG^o < 0, what is K

A

K>1

238
Q

if changeG^o > 0, what is K

A

K<1

239
Q

if changeG^o = 0, how does the system need to shift to reach equilibrium

A

no shift, it is at equilibrium

240
Q

if changeG^o < 0, how does the system need to shift to reach equilibrium

A

shift right

241
Q

if changeG^o > 0, how does the system need to shift to reach equilibrium

A

shift left

242
Q

for an exothermic reaction, what is the relationship between K and T

A

inversely proportional

243
Q

for an endothermic reaction, what is the relationship between K and T

A

directly proportional

244
Q

what is the van’t hoff equation used for

A

to calculate K at any temp once changeH^o and K are known at a given temperature

245
Q

what is the maximum possible useful work obtainable from a process at constant temp and pressure

A

the change in free energy

246
Q

For a non-spontaneous process, what does the value of changeG tell us

A

the minimum amount of work that must be expended to make the process occur

247
Q

is useful work = 0, what does this mean for qp and changeH

A

qp = changeH

248
Q

if useful work = maximum useful work, what does that mean for qp and TchangeS

A

qp = TchangeS

249
Q

what happens in any real cyclic process

A

work is changed to heat in the surroundings and the entropy of the universe increases

250
Q

why is the availability of useful energy an increasing problem

A

when energy is used to do work, it becomes less organized and less concentrated, and thus less useful

251
Q

what is an adiabatic process

A

a process in which no energy as heat flows into or out of the system

252
Q

for an adiabatic process, what does q equal?

A

0

253
Q

for an adiabatic process, what does changeE equal

A

w

254
Q

for an adiabatic process, what is the source of the energy

A

the thermal energy of the gas; the temp of the gas decreases to furnish the energy to do the work

255
Q

for a reversible isothermal expansion, what is the relationship between PxV

A

PV = constant

256
Q

for a reversible adiabatic expansion, what is the relationship between PxV^(Cp/Cv)

A

PxV^(Cp/Cv) = constant

257
Q

what is the common ion effect

A

the shift in equilibrium position that occurs b/c of the addition of an ion already involved in the equilibrium reaction

258
Q

do common ions increase or decrease solubility

A

decrease

259
Q

what is a buffered solution

A

one that resists a change in pH when either hydroxide ions or protons are added

260
Q

what is a buffer

A

a weak acid and its salt (weak base partner) or a weak base and its weak acid partner

261
Q

when doing calculations for a buffered solution when a strong acid or base is added, what should you do

A
  1. assume it goes to completion and carry out the stoichiometric calculations (SRE chart)
  2. carry out the equilibrium calculations (ICE chart)
262
Q

when doing calculations for a normal buffered solution, what should you do

A

decide what species are at play, write the appropriate reaction (doesn’t matter if from acid or base perspective), make ICE chart, solve for x

263
Q

how do buffers work

A

when we ‘harass’ a buffer with OH-, the OH- are not allowed to accumulate in solution; instead, they get reacted with the weak base and pull the H+ out of solution to make H2O

264
Q

in a good buffer, what happens to the ratio of [HA]/[A-]

A

it doesn’t change much; the goal of a good buffer is to keep that ratio as constant as possible

265
Q

what is the henderson hasselbalch equation

A

pH = pKa + log([A-]/[HA]; useful for calculating the pH of a buffered solution when the ratio [HA]/[A-] is known

266
Q

what is Ksp

A

the solubility product constant/solubility product

267
Q

what is the general form of a Ksp expression

A

Ksp = [ion 1][ion 2]; if any ions have coefficients, their concentrations are raised to that power

268
Q

does the amount of excess solid present in solution or the size of the particles effect the equilibrium position

A

no

269
Q

what is the difference between the solubility of a given solid and its solubility product

A

the solubility product is an equilibrium constant, and thus has only one value for a given solid at a given temp; solubility is an equilibrium position and has an infinite number of possible values at a given temp, depending on the other conditions (like the presence of a common ion, etc)

270
Q

If two salts produce the same number of ions, how can we find which is more soluble

A

we can decide which is more soluble by comparing their Ksp values (bigger means more soluble)

271
Q

if two salts produce different numbers of ions, how can we find which is more soluble

A

you just have to calculate their solubilities to compare them

272
Q

can the pH of a solution affect a salt’s solubility

A

yes, quite significantly

273
Q

if the anion X- is an effective based, what happens to its salt’s (MX) solubility in acidic solution

A

it increases

274
Q

how can we decide whether or not a ppt will form in a solution

A

find Q, which is found the same was as Ksp, except that the initial concentrations are used instead of equilibrium concentrations

275
Q

if Q > Ksp, will a ppt form

A

yes

276
Q

if Q < Ksp, will a ppt form

A

no

277
Q

how do we calculate the equilibrium concentrations in the solution after a ppt is complete

A
  1. first find Q to decide if a ppt will form in the first place
  2. assume the reaction between the ions left in solution goes to completion; perform stoichiometry calculations (an SRE chart, use moles) to find how many ions of each are in solution before the reaction proceeds to equilibrium
  3. do equilibrium calculations (ICE chart, using molarities), solve for x
278
Q

what is selective precipitation

A

a method of separating metal ions in aqueous solution by using a reagent who’s anion forms a ppt with only one of the metal ions in the mixture

279
Q

what is a complex ion

A

a charged species consisting of a metal ion surrounded by ligands

280
Q

what is a ligand

A

a molecule or an ion having a lone pair of electrons that can be donated to the metal ion to form a covalent bond

281
Q

what are some common ligands

A

water, NH3, Cl-, CN-

282
Q

when complex ions are formed, in which way does equilibrium shift

A

to the right; solubility of slightly soluble ionic compound goes up

Chem (20 decks)

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