gchem 2 Flashcards by maddie kim

What is convection?

fluid movement caused by hotter portions of a fluid rising and the cooler portions of the fluid sinking

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What is radiation?

electromagnetic waves emitted from a hot body into the surrounding environment

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What is a black body radiator?

theoretically perfect body that absorbs all energy incident upon it and emits 100% of this energy as electromagnetic radiation

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What is conduction?

molecular collisions carry heat along a conduit

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What is heat capacity?

the amount of energy a system must absorb to give a unit change in temperature (J/K or cal/degrees celcius)

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What is the formula for heat capacity?

C = q/∆T

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What is the formula for specific heat?

q=mc∆T

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What is the specific heat of water?

1.0 cal/g ̊C

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What is the purpose for calorimeters?

To calculate enthalpy change

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How to solve coffee cup calorimeter problems

q=mc∆T

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How to solve bomb calorimeter problem

q = C∆T

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Which type of calorimeter provides constant pressure and which provides constant volume?

bomb -constant volume

coffee- constant pressure (atmospheric)

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What is pressure - volume work?

change in volume at constant pressure

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On a pressure vs. volume graph, what represents the pv work?

The area under the curve

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What is the first law of thermodynamics?

energy can neither be created or destroyed

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work done on the system is ___, work done by the system is ___

positive, negative

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What is the second law of thermodynamics?

heat cannot be changed completely into work in a cyclical process

entropy in an isolated system can never decrease

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What is the third law of thermodynamics?

pure crystalline substances at absolute zero have an entropy of zero

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What is the zeroth law of thermodynamics?

everything tends to move toward thermal equilibrium with everything else. (2 objects in thermal equilibrium = same temperature)

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What is the definition for temperature?

the average kinetic energy of molecules

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What equation shows the direct relationship between temperature and kinetic energy?

KE = 3/2kBT (where kB is Boltzmann’s constant)

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How to convert celcius to Kelvin

add 273.15 to celcius

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What is enthalpy?

the energy contained within chemical bonds

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What is standard state?

a set of specific conditions as the reference point for measuring and reporting enthalpy, entropy, and Gibbs free energy

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How to calculate ΔHRXN Using Bond Energies

add up the bond energies of all of the products and reactants. If a bond is broken during the reaction, energy is required, so the bond energy should be given a positive sign. If a bond is formed, energy is released, so the bond energy should be given a negative sign. Once again, multiply all bond energy values by their coefficients in the balanced equation.

ΔHcombustion

A high heat of combustion is associated with an unstable molecule and a low heat of combustion with a stable molecule.

ΔHformation

The enthalpy value for the formation of a compound from its elements in their standard states. If the number is negative, formation is an exothermic process, if it is positive, the process is endothermic.

ΔHsolution

The enthalpy value associated with the dissolution of a species into solution. We’ll discuss this in more detail when we cover solution chemistry.

ΔHvaporization

The enthalpy value associated with the phase change from liquid to gas. The reverse process (condensation) simply interchanges products and reactants and thus the sign is just changed.

ΔHfusion

The enthalpy value associated with the phase change from liquid to solid. The sign changes for the reverse process (melting)

What is entropy?

a measure of randomness or disorder in a system

Entropy increases with 5 factors increasing?

number of items, volume, temperature, disorder, complexity

What is gibb's free energy?

∆G = the amount of “free” or “useful” energy available to do work

What does isobaric mean?

constant pressure

What does isothermal mean?

no heat exchange

What is the fundamental thermodynamic relation?

∆G = ∆H - T∆S

If ∆H is positive and entropy change is negative, what will the sign of ∆G be?

positive

If the change in entropy is positive, and enthalpy is negative, the reaction is :

spontaneous

If a reactant is dissolved in a solution, causing the temp to increase, the ΔG for this reaction is __

negative

What equation relates Gibbs free energy to equilibrium?

∆G° = - RTlnKeq Keq = e^ -ΔG/RT

Arrhenius acid/ base definition

acids- produce H+ ions in solution | base- produce OH- ions in solution

Bronsted Lowry acids/bases

acids - donate protons | bases - accept protons

Lewis acid/bases

acid - accept pair of electrons | base- donate pair of electrons

What is the definition of amphoteric ?

substances can act as either an acid or base | eg H2O

Calculate pH with H+ concentration

pH= -log (H+)

What is the equation for Kw?

Kw=[H3O+][OH-]=10^ -14

Formula for acid dissociation constant

Ka = [H+][A-]/[HA]

If Ka is greater than one, that means the acid is __

strong

What is the formula for base dissociation?

Kb = [OH-][HA]/[A-]

Smaller Kb indicates that an acid is __

strong

Addition of either an acid or base to water shifts the equilibrium for the ionization of water to which direction?

left

How to calculate the pH for weak acids

1. write out balanced eq 2. ICE table 3. solve for x 4. -log(H+)

all strong acids and bases dissociate __ percent in water

100

What are the strong acids?

HI, HBr, HCl, HNO3, HClO4, HClO3, H2SO4, h3O+

What are the strong bases?

Group 1A hydroxides, NH2-, H-, Ca(OH)2, Sr(OH)2, Ba(OH)2, Na2O, CaO

If an acid has a Ka less than 1, than it is __

weak

If a base has a Kb less than one, it is a ___ base

weak

What does the "salt of a weak acid" refer to?

conjugate base of the weak acid combined with a cation

What does the "salt of a weak base" refer to?

conjugate acid combined with an anion to form a salt

What does the term "equivalent" mean when it comes to titration?

the amount of acid or base necessary to produce or consume one mole of [H+] ions

On a titration curve, what is one the x-axis and what is on the y-axis?

x-axis - volume of titrant | y-axis - pH

What is the difference between an analyte and a titrant?

analyte - in beaker | titrate - added dropwise

For SA and SB, at the equivalence point, ____

[H+] = [OH-]

At the equivalent point/stoichiometric point, the [titrant]= __

[analyte]

What is the pH of the equivalent points for WB w SA, WA w SB, SA w SB, WA w WB?

For WB w/ SA: pH < 7 For WA w/ SB: pH > 7 For SA w/ SB: pH about 7 For WB w/ WA: pH about 7

half equivalence point = ____ on graph

midpoint of nearly horizontal section

at half equivalence point, [HA] ___

[HA] = [A-]

What are indicators?

weak acids that change color as they dissociate. To set up a titration, you should know the approx. pH of equivalence point to select an indicator that will change color at that pH

Difference between the end point and equivalence point?

end point - when indicator causes color change | equivalent - when [titrant] = [analyte]

Where is the buffer region?

nearly horizontal area surrounding the half-equivalence point

What is the Henderson -Hasselbalch equation?

pH = pKa + log[A-]/[HA]