chem 0330 - midterm 1 Flashcards
what are the solubility rules
- most nitrate salts are soluble
- most salts of sodium, potassium, and ammonium are soluble
- most chloride salts are soluble. exceptions: silver chloride, lead chloride, mercury chloride
- most sulfate salts are soluble. exceptions: barium sulfate, lead sulfate, calcium sulfate
- most hydroxide salts are only slightly soluble. exceptions: sodium hydroxide, potassium hydroxide, and calcium hydroxide (marginally soluble)
- most sulfide, carbonate, and phosphate salts are only slightly soluble
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
it lies far to the right
what is the term for a reaction in which the equilibrium position favors the reactants such that the reaction barely appears to have happened?
it lies far the left
what are the two possible reasons why the concentrations of the reactants and products of a given reaction remain unchanged when mixed
- the system is at equilibrium
2. the fwd and reverse reactions are so slow that the system moves toward equilibrium at an undetectable rate
what is the law of mass action
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
what is the equilibrium expression for a reaction written in reverse
the reciprocal of that for the original equation
what is the equilibrium expression for a reaction in which the balanced equation is multiplied by a factor of n
the original expression raised to the nth power
in which cases must corrections for non-ideal behavior be applied to the law of mass action
- concentrated aqueous solutions
2. gasses at high pressures
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?
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
in what other way can the equilibrium expression be written
in terms of the equilibrium partial pressures of the gases; Kp represents an equilibrium constant in terms of partial pressures
what is the relationship between K and Kp
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
what are homogenous equilibria
systems in which all reactants and products are in the same phase
what are heterogenous equilibria
equilibria that involve more than one phase
how do we treat pure solids or liquids involved in a chemical reaction when creating the equilibrium expression
if pure solids or pure liquids are involved in a chemical reaction, their concentrations are not included in the expression for the reaction
what does knowing the equilibrium constant for a reaction allow us to predict
- 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
what indicates the inherent tendency for a reaction to occur
the magnitude of the equilibrium constant
what does a value of K much larger than 1 mean
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
what does a very small value of K mean
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
are the size of K and the time required to reach equilibrium directly related
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
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
- 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
how is the reaction quotient obtained
by applying the law of mass action, but using initial concentrations instead of equilibrium concentrations
to determine in which direction a system will shift to reach equilibrium, we compare the values of Q and K
- 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
how can we make the math simpler when doing equilibrium calculations
if K is super small, we can can eliminate it
how can we quantitatively predict the effects of changes in concentration, pressure, and temperature on a system at equilibrium
by using Le Châtelier’s principle
what is Le Châtelier’s principle
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
what is the effect of a change in concentration on a system at equilibrium
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
what is the effect of the addition of an inert gas on a system at equilibrium
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
what is the effect of a change in volume of the container of a system at equilibrium
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
does the K value change with temperature
YES
what is the effect of adding heat (increasing temp) to an exothermic system (energy is a product) at equilibrium
the reaction shifts left, increasing the concentrations of the products, decreasing the value of K
what is the effect of adding heat (increasing temp) to an endothermic system (energy is a reactant) at equilibrium
the reaction shifts right, increasing the concentrations of the reactants, increasing the value of K
what is an acid
a proton donor
what is a base
a proton acceptor
what is a conjugate base
what remains of the original acid molecule after a proton is lost
what is a conjugate acid
the product formed when a proton is transferred to a base
what is Ka
the acid dissociation constant; only used to represent a reaction in which a proton is removed from HA to form the conjugate base A-
where does the equilibrium lie for a strong acid
far to the right; almost all original HA is dissociated at equilibrium
what are the strong acids
- HCl - hydrochloric acid
- HNO3 - nitric acid
- HBr - Hydrobromic acid
- H2SO4 - sulfuric acid
- HI - hydroiodic acid
- HClO4 - perchloric acid
what type of acid yields a weak conjugate base
a strong acid
where does the equilibrium lie for a weak acid
far to the left; most of the acid originally placed in solution is still present as HA at equilibrium
what type of acid yields a strong conjugate base
a weak acid
is Ka large or small for a strong acid
large
is Ka large or small for a weak acid
small
how does the strength of water as a base compare to the strength of the conjugate base of a strong acid
water is stronger
how does the strength of water as a base compare to the strength of the conjugate base of a weak acid
water is weaker
what does Kw represent
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
what is the value of Kw (at 25 degrees C)
1 x 10 ^-14
describe a solution in which [H+] = [OH-]
neutral, both concentrations = 1x10^-7
describe a solution in which [H+] > [OH-]
acidic
describe a solution in which [H+] < [OH-]
basic
what is pH equal to
-log[H+]
what is pOH equal to
-log[OH-]
what is pK equal to
-logK
how do you do sig figs for logs
the number of decimal places in the log is equal to the number of sig figs in the original number
what is pH + pOH always equal to (for any aqueous solution at 25 degrees celsius)
14
what should always be the first step in solving acid-base problems
writing the major species present in the solution
how should you calculate the pH of a strong acid solution
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
how should you calculate the pH of a weak acid solution
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
how should you calculate the pH of a mixture of weak acids
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.
what is the percent dissociation of a strong acid
assumed to be 100%
what is the percent dissociation of a weak acid
amount dissociated/initial concentration x 100
for a weak acid, how are the percent dissociation and the concentration of the acid related
the percent dissociation increases as the acid becomes more dilute
what are the strong bases
sodium hydroxide, potassium hydroxide, group 1 hydroxides, group two hydroxides are strong but not very soluble
how should you calculate the pH of a strong base
determine the major OH- contributor. assume 100% dissociation and calculating pOH. then find pH by subtracting pOH from 14.
what is Kb
the base dissociation constant; always refers to the reaction of a base with water to form the conjugate acid and the hydroxide ion
how should you calculate the pH of a weak base
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
what are polyprotic acids
acids that can furnish more than one proton per molecule
how do polyprotic acids dissociate
in a stepwise manner, one proton at a time
when deciding whether a solution is acidic, neutral, or basic, Ka > Kb means it is
acidic
when deciding whether a solution is acidic, neutral, or basic, Ka = Kb means it is
neutral
when deciding whether a solution is acidic, neutral, or basic, Ka < Kb means it is
basic
how can you calculate the fractions of the various species present in a solution of a polyprotic acid
the fraction of each species is the concentration of that species divided by the total concentrations of all species
how do the Ka1, Ka2, … Kaj values for a typical weak polyprotic acid compare
Ka1 > Ka2 > … > Kaj
how can you calculate the pH of a solution of a polyprotic acid
typically, only the first dissociation step is important in determining the pH, so just treat that reaction as a typical weak acid problem
what is special about sulfuric acid
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
how do salts that consist of the cations of strong bases and the anions of strong acids affect [H+] when dissolved in water
they don’t; thus, aqueous solutions of salts like KCl, NaCL, NaNO3, and KNO3 are neutral
how do alkali metal ions affect pH
they don’t
how are Ka and Kb related for any weak acid and its conjugate base?
Ka x Kb = Kw
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?
basic
a salt whose cation is the conjugate acid of a weak base produces an [acidic/basic/neutral] solution?
acidic
what is the significance of a highly charged metal ion in a salt
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
what is energy
the capacity to do work or to produce heat
what is the law of conservation of energy
energy can be converted from one form to another but can be neither created nor destroyed; the energy of the universe is constant
what are the two types of energy
Potential and kinetic
what is potential energy
energy due to position or composition
what is kinetic energy
energy due to the motion of the object and depends on the object’s mass and velocity
what is temperature
a property that reflects the random motions of the particles in a particular substance
what is heat
involves the transfer of energy between two objects due to a temperature difference
what is work
force acting over a distance
what are the two ways to transfer energy
through work and through heat
is energy a state or a path function
state
is work a state or a path function
path
is heat a state or a path function
path
what is a state function
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
what is the system
the part of the universe on which we wish to focus attention
what are the surroundings
everything else in the universe thats not the system
what is an exothermic reaction
when a reaction results in the evolution of heat; energy flows out of the system
what is an endothermic reaction
reactions that absorb energy from the surroundings; heat flows into a system
where does the energy, released as heat, come from in an exothermic reaction?
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
what does the change in PE stored in the bonds of the product compared to the bonds of the reactants represent
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.
in an exothermic process, how do the bonds of the products compare to the bonds of the reactants
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
does making a bond absorb or release energy
release
does breaking a bond absorb or release energy
absorb
in an endothermic reaction, what is the energy that flows into the system (as heat) used to do
to increase the PE of the system
in an exothermic reaction, do the products or the reactants have a higher PE
reactants
in an endothermic reaction, do the products or the reactants have a higher PE
products
in an endothermic reaction, how do the bonds of the products compare to the bonds of the reactants
the bonds of the products are weaker (on average)
what is the first law of thermodynamics
the law of conservation of energy; the energy of the universe is constant
how can the internal energy of a system be changed
by a flow of work, heat, or both
what two parts do thermodynamic quantities always consist of
a number and a sign
what does the sign in a thermodynamic quantity reflect
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
if the system does work on the surroundings, what sign does w get
negative
if the surroundings do work on the system, what sign does w get
positive
why do work and P(change in V) have opposite signs
b/c when the gas expands (changeV is positive), work flows into the surroundings (w is negative), and vice versa
what is the work accompanying a change in volume of a gas often called
PV work
in dealing with PV work, what does the P refer to
external pressure; the pressure that causes a compression or that resists an expansion
what does the variable q stand for
heat
what is the variable for enthalpy
H
is enthalpy a state or a path function
a state function
a process carried out at constant pressure only allows what kind of work to take place
PV work
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
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
if the products of a reaction have greater enthalpy than the reactants, is change in enthalpy positive or negative
positive; heat is absorbed, rxn is endothermic
if change in enthalpy is positive (at constant P), is the reaction exothermic or endothermic
endothermic
if the reactants of a reaction have greater enthalpy than the products, is change in enthalpy positive or negative
negative; heat is released, rxn is exothermic
if change in enthalpy is negative (at constant P), is the reaction exothermic or endothermic
exothermic
what is the only way to change the kinetic energy of an ideal gas
change its temperature
what is the molar heat capacity of a substance
the energy required to raise the temp of 1 mole of that substance by 1 kelvin
if an ideal gas is heated in a rigid container, is there PV work? why or why not?
no, because there is no change in volume, so change in v = 0
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?
to increase the translational energies of the gas molecules
what is the variable for molar heat capacity
C
what is Cv (molar heat capacity of an ideal gas at a constant volume)
(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
what is different about heating a gas at constant pressure vs constant volume
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
what is Cp (the heat required to increase the temp of 1 mole of gas by 1 K at constant P)
(3/2)R + R = (5/2)R
or
Cv + R = Cp
why do polyatomic gases have a Cv greater than (3/2)R
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)
is the larger Cv for polyatomic gases related to whether or not the gas is behaving ideally
no
what is the equation for when a gas is heated at constant volume
change in E = Cv(change in T)
what is the equation for when a gas is heated at constant pressure
“heat” required = nCv(change in T)
what is the equation for change in enthalpy, regardless of any conditions on pressure or volume
change in enthalpy = nCp(change in T)
what is the only thing that the enthalpy of an ideal gas depends on
Temperature
what equation is used to calculate the heat flow of an ideal gas
q = mC(change in T), where Cv or Cp is used, depending on the conditions
at constant volume, what is heat flow equal to
change in E
at constant pressure, what is heat flow equal to
change in H
what is a calorimeter
a device used to determined the heat associated with a chemical reaction
what is calorimetry
the science of measuring heat
what is the heat capacity of a substance
C = heat absorbed/increase in temp
what is specific heat capacity
the energy required to raise the temp of 1g a substance by 1 degree celsius
what is molar heat capacity
the energy required to raise the temp of 1 mole of a substance by 1 degree celsius
what is constant pressure calorimetry used for
determining the changes in enthalpy occurring in solution b/c under conditions of constant pressure the change in enthalpy = the heat
if two reactants at the same temp are mixed and the resulting solution gets warmer, is the reaction exothermic or endothermic
exothermic
if two reactants at the same temp are mixed and the resulting solution gets cooler, is the reaction exothermic or endothermic
endothermic
is any work done in constant pressure calorimetry (reactions in solution)
no b/c change in volume is 0
in constant pressure calorimetry, what 3 quantities are equal
change in E, change in H, and q
for a reaction involving gases at constant pressure, are change in E and change in H always equal?
no
for an ideal gas, when is the only time that work occurs
when volume changes
is work done in calorimetry experiments performed at constant volume
no
what is Hess’s Law
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
what are two important things to remember when using hess’s law
- if a reaction is reversed, the sign of changeH is also reversed
- if coefficients in a balanced reaction are multiplied by an integer, changeH must also be multiplied by that integer
what is the standard enthalpy of formation of a compound
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
what is the standard state for a substance
a precisely defined reference state
what symbol indicates that the corresponding process has been carried out under standard conditions
the superscript 0
what is the standard state for a gas
a pressure of exactly 1 atm
what is the standard state for a substance present in a solution
a concentration of exactly 1 M at an applied pressure of 1 atm
what is the standard state for a pure substance in a condensed state (liquid or solid)
the pure liquid or solid
what is the standard state for an element
the form in which the element exists (is most stable) under conditions of 1 atm and the temp of interest (usually 25 degrees C)
how can the enthalpy change for a given reaction be calculated
by subtracting the enthalpies of formation of the reactants from the enthalpies of formation of the products
are elements in their standard states included in the changeHreaction calculations
no; change in standard enthalpy of formation for an element in its standard state is 0
what does it mean for a process to be spontaneous
if it occurs without outside intervention
what is the driving force of all spontaneous processes
an increase in entropy
what does the probability of occurrence of a particular arrangement (state) depend on
the number of ways (microstates) in which
what is the formula to determine the number of microstates for a given arrangement
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
rank solid, liquid, and gas in order from least to most entropy
Solid < liquid < gas
what is an isothermal process
one in which the temperatures of the system and the surroundings remain constant at all times
for any isothermal process involving an ideal gas, what is the change in energy equal to
0
for any isothermal process involving an ideal gas, what is heat (q) equal to
-w (negative work)
what is a free expansion
one in which no work is done in expanding the volume of a gas
what is work equal to in a free expansion
0
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
they are essentially equal
what is a process carried out so that the system is always at equilibrium called
a reversible process
as the number of steps in an isothermal gas expansion increases, what happens to the work
it also increases
what is the maximum work that a given amount of gas can perform in going from V1 to V2 at constant temperature
it occurs in the reversible expansion; wmax = wrev = nRT(ln(V2/V1))
as the number of steps in the isothermal compression of a gas increases, what happens to the work required to compress the gas
it also decreases
what is the significance of expanding/compressing a gas reversibly (in an infinite number of steps)
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
what happens to work in any finite-step, cyclic expansion-compression process
work is always converted to heat
what is the relationship between the input of work and the output of work in an irreversible cyclic process
more work must be input to the system than the system produces
are all real processes reversible or irreversible
irreversible
when does the maximum work obtainable from the gas occur
when the expansion is carried our reversibly
what is a reversible cyclic process
one in which both the system and the surroundings are returned exactly to their original conditions
what is an irreversible process
one in which even when the system is cycled and thus returned to its original state, the surroundings are changed in a permanent way
what is the only condition in which a reversible process can occur
equilibrium
what is the second law of thermodynamics
in any spontaneous process, there is always an increase in the entropy of the universe; the entropy of the universe is increasing
how can we predict whether a given process will be spontaneous
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
in an endothermic process, what is the direction of heat flow
out of the surroundings and into the system
in an exothermic process, what is the direction of heat flow
out of the system and into the surroundings
does an exothermic process in the system increase or decrease the entropy of the surroundings
increase
does an endothermic process in the system increase or decrease the entropy of the surroundings
decrease
what does the sign of changeSsurroundings depend on
the direction of the heat flow
what does the magnitude of changeSsurroundings depend on
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
at constant pressure and temperature, changeSsurroundings is equal to what
-(changeH)/T
what is free energy defined as
G, G = H - TS
what is the equation for changeSuniverse as related to G at constant T and P
changeSuniverse = -(changeG)/T
when will a process carried out at constant temp and pressure be spontaneous
only if changeG is negative
a process at constant T and P is spontaneous in which direction
in which the free energy decreases
how can entropy changes of the system in chemical reactions be predicted
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
if the number of molecules of the gaseous products > the number of molecules of the gaseous reactants, what does this mean for changeS
changeS is positive for that reaction; vice versa is also true
on a fundamental level, what does the change in enthalpy determine
whether a reaction is exothermic or endothermic at constant pressure
on a fundamental leve, what does change in free energy determine
whether a process is spontaneous at constant temp and pressure
what is the third law of thermodynamics
the entropy of a perfect crystal at 0 K is 0; a perfect crystal represents the lowest possible entropy
does the entropy of a substance increase or decrease with temperature
increase
which equation is used at the melting point or boiling point to account for the entropy change that accompanies the change of state
changeS = changeH/T
what do standard entropy values represent
the increase in entropy that occurs when a substance is heated from 0K to 298K at 1atm
how can the entropy change for a given chemical reaction be calculated
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
how is molecular complexity related to standard entropy value
the more complex the molecule, the higher the standard entropy value
what is the standard free energy change
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
why is it useful to know changeG^o for a reaction
knowing changeG^o values for several reactions allows us to compare the relative tendency of these reactions to occur
the more negative the value of changeG^o….
the further a reaction will go to the right to reach equilibrium
does changeG^o tell us anything about the rate of reaction
no; it only tells us about its eventual equilibrium position
is free energy a state or path function
state
what is the standard free energy of formation of a substance
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
what is the standard free energy of formation of an element in its standard state
0
what do a negative large magnitude of changeG^o indicate
that the reaction is very favorable thermodynamically
a reaction system at constant temp and pressure will proceed spontaneously in which direction
the direction that lowers its free energy
why do reactions proceed until they reach equilibrium
b/c a reaction system at constant temp and pressure will proceed spontaneously in the direction that lowers its free energy
what is the lowest free energy value available to a particular reaction system
the equilibrium position
why does the free energy of a reaction system change as the reaction proceeds
b/c free energy depends on the pressure of a gas (or on the concentration of species in solution)
for an ideal gas is enthalpy pressure-dependent
no
for an ideal gas, is entropy pressure-dependent
yes b/c it depends on volume
at a given temp for a mole of ideal gas, what gives the gas greater entropy, large volume or small volume?
large volume; S(large volume) > S(small volume)
at a given temp for a mole of ideal gas, what gives the gas greater entropy, high pressure or low pressure?
low pressure; S(low pressure) > S(high pressure)
if a reaction system has a negative changeG, does that mean that the system will proceed to completion
no, it will go to equilibrium, because the equilibrium position is the lowest possible free energy available to it
if a phase change reaction has a negative changeG, will that phase change go to completion
yes, because the end of the phase change has the lowest free energy; there is no intermediate substance with lower free energy
where does the equilibrium point for a reaction system occur
at the lowest value of free energy available to the reaction system
why is the point of minimum free energy for a reaction system the equilibrium point
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
what does it mean when changeG^o equals zero for a particular reaction
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
what does it mean when changeG^o < 0
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
what does it mean when changeG^o > 0
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.
if changeG^o = 0, what is K
1
if changeG^o < 0, what is K
K>1
if changeG^o > 0, what is K
K<1
if changeG^o = 0, how does the system need to shift to reach equilibrium
no shift, it is at equilibrium
if changeG^o < 0, how does the system need to shift to reach equilibrium
shift right
if changeG^o > 0, how does the system need to shift to reach equilibrium
shift left
for an exothermic reaction, what is the relationship between K and T
inversely proportional
for an endothermic reaction, what is the relationship between K and T
directly proportional
what is the van’t hoff equation used for
to calculate K at any temp once changeH^o and K are known at a given temperature
what is the maximum possible useful work obtainable from a process at constant temp and pressure
the change in free energy
For a non-spontaneous process, what does the value of changeG tell us
the minimum amount of work that must be expended to make the process occur
is useful work = 0, what does this mean for qp and changeH
qp = changeH
if useful work = maximum useful work, what does that mean for qp and TchangeS
qp = TchangeS
what happens in any real cyclic process
work is changed to heat in the surroundings and the entropy of the universe increases
why is the availability of useful energy an increasing problem
when energy is used to do work, it becomes less organized and less concentrated, and thus less useful
what is an adiabatic process
a process in which no energy as heat flows into or out of the system
for an adiabatic process, what does q equal?
0
for an adiabatic process, what does changeE equal
w
for an adiabatic process, what is the source of the energy
the thermal energy of the gas; the temp of the gas decreases to furnish the energy to do the work
for a reversible isothermal expansion, what is the relationship between PxV
PV = constant
for a reversible adiabatic expansion, what is the relationship between PxV^(Cp/Cv)
PxV^(Cp/Cv) = constant
what is the common ion effect
the shift in equilibrium position that occurs b/c of the addition of an ion already involved in the equilibrium reaction
do common ions increase or decrease solubility
decrease
what is a buffered solution
one that resists a change in pH when either hydroxide ions or protons are added
what is a buffer
a weak acid and its salt (weak base partner) or a weak base and its weak acid partner
when doing calculations for a buffered solution when a strong acid or base is added, what should you do
- assume it goes to completion and carry out the stoichiometric calculations (SRE chart)
- carry out the equilibrium calculations (ICE chart)
when doing calculations for a normal buffered solution, what should you do
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
how do buffers work
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
in a good buffer, what happens to the ratio of [HA]/[A-]
it doesn’t change much; the goal of a good buffer is to keep that ratio as constant as possible
what is the henderson hasselbalch equation
pH = pKa + log([A-]/[HA]; useful for calculating the pH of a buffered solution when the ratio [HA]/[A-] is known
what is Ksp
the solubility product constant/solubility product
what is the general form of a Ksp expression
Ksp = [ion 1][ion 2]; if any ions have coefficients, their concentrations are raised to that power
does the amount of excess solid present in solution or the size of the particles effect the equilibrium position
no
what is the difference between the solubility of a given solid and its solubility product
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)
If two salts produce the same number of ions, how can we find which is more soluble
we can decide which is more soluble by comparing their Ksp values (bigger means more soluble)
if two salts produce different numbers of ions, how can we find which is more soluble
you just have to calculate their solubilities to compare them
can the pH of a solution affect a salt’s solubility
yes, quite significantly
if the anion X- is an effective based, what happens to its salt’s (MX) solubility in acidic solution
it increases
how can we decide whether or not a ppt will form in a solution
find Q, which is found the same was as Ksp, except that the initial concentrations are used instead of equilibrium concentrations
if Q > Ksp, will a ppt form
yes
if Q < Ksp, will a ppt form
no
how do we calculate the equilibrium concentrations in the solution after a ppt is complete
- first find Q to decide if a ppt will form in the first place
- 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
- do equilibrium calculations (ICE chart, using molarities), solve for x
what is selective precipitation
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
what is a complex ion
a charged species consisting of a metal ion surrounded by ligands
what is a ligand
a molecule or an ion having a lone pair of electrons that can be donated to the metal ion to form a covalent bond
what are some common ligands
water, NH3, Cl-, CN-
when complex ions are formed, in which way does equilibrium shift
to the right; solubility of slightly soluble ionic compound goes up
