Kaplan Chemistry: Chapter 7 Thermochemistry

Question 1

Change in internal energy system

Answer 1

delaU = Q-W
Q = heat
W = work done BY system

Question 2

what does U equal in an isothermal process.

Answer 2

isothermal process = constant temp, meaning that U is CONSTANT.
deltaU = 0 = Q-W
therefore, Q = W

Question 3

what does the area in a P vs V graph signify

Answer 3

the work done by the system, and the heat that entered the system

Question 4

in an adiabatic process, what is delta U equation?

Answer 4

adiabatic: no heat is exchanged. therefore, Q=0, meaning that deltaU=-W

Question 5

in a P vs V graph, and adiabatic process appears to be:

Answer 5

hyperbolic

Question 6

what does a P vs V graph look like in an isobaric process?

Answer 6

isobaric = pressure is constant. isobaric processes are horizontal lines.

Question 7

what does a P vs V graph look like in an isochoric process?

Answer 7

isochoric = isovolumetric = constant volume. W =0. therefore, deltaU = Q –> change in interanl energy is equal to the heat added to the system.

• in a P vs V graph, an isovolumetric processes causes a VERTICAL LINE, meaning that the WORK is 0 because work is the area of a Pvs V graph.

Question 8

state functions

Answer 8

Pressure, Density, temperature, volume, enthalpy, internal energy (U), free energy (G), and entropy (S)

Question 9

standard conditions

Answer 9

25C (298K), 1atm pressure, 1M concentrations.

Question 10

when are standard conditions used?

Answer 10

kinetics, equilibrium, and thermodynamic problems

Question 11

STP conditions

Answer 11

0C (273K), 1 atm pressure.

Question 12

when are STP conditions used?

Answer 12

used for ideal gas calculations.

Question 13

entropy and enthalpy ____ with temperature

Answer 13

INCREASES with temperature

Question 14

entropy and enthalpy ____ as a material changes phase from solid –> liquid –> gas

Answer 14

increases.

Question 15

sublimation means

Answer 15

solid to gas, by passes liquid stage

Question 16

deposition means

Answer 16

gas to solid, by passes the condensation to liquid stage.

Question 17

true definition of enthalpy

Answer 17

heat (Q) under a constant pressure, which is an assumption that is usually made for thermodynamic problems.

Question 18

equation for heat absorbed or released in a given process

Answer 18

Q = mcdeltaT

Question 19

units for a newton

Answer 19

kgm/s^2

Question 20

units for a joule

Answer 20

1J = Nm = (kgm^2)/s^2

Question 21

heat of a substance when it is undergoing a phase change

Answer 21

q=mL
L= latent heat capacity.
temp remains constant as the compound is converted to the next phase. once the entire sample is converted, then the temperature begins to rise again.

Question 22

enthalpy/heat changes at a constant pressure equation

Answer 22

delta H = H(products)-H(reactants)

Question 23

enthalpy of formation of pure elements

Answer 23

0

Question 24

what is the standard heat of reaction? formula?

Answer 24

the enthalpy change accompanying a reaction being carried out under standard conditions
deltaHrxn = sumHformation(products)- sumHformation(reactants)

Question 25

Hess’s Law and equation

Answer 25

enthalpy changes of reactions are additive

delta Hrxn = HbondsBROKEN - Hbondsformed.

Question 26

longer hydrocarbons produce more combustion products and release ____ heat.

Answer 26

release more heat. that is, longer hydrocarbon combustion is more exothermic.

Question 27

Entropy formula in relation to Q and temperature

Answer 27

S = Q/T
Q = heat that is gained or lost in a reversible process.

Question 28

Gibbs free energy equation involving H, T and S

Answer 28

G = H - TS

Question 29

if H is -, and S is +, the reaction is ____ (spon/nonspon)

Answer 29

spontaneous

Question 30

if H is +, and S is -, the reaction is ____ (spon/nonspon)

Answer 30

NEVER spontaneous

Question 31

if H is -, and S is -, the reaction is ____ (spon/nonspon)

Answer 31

spontaneous at LOW temp

Question 32

if H is +, and S is +, the reaction is ____ (spon/nonspon)

Answer 32

spontaneous at HIGH TEMP

Question 33

what does it mean when deltaG is 0

Answer 33

the reaction is in equilibrium.

Question 34

equation for gibbs free energy when the reaction is not taking place under standard state.

Answer 34

G = Go + RTlnKeq

recall: Go = -RTlnKeq

Question 35

The relative thermodynamic stability of isomeric organic compounds can be inferred from which of the following types of experimental data?

A.Boiling points
B.UV–visible absorption spectra
C.Mass spectroscopic fragmentation patterns
D.Heats of combustion

Answer 35

Heats of Combustion
The question stem is asking about thermodynamic stability, or chemical energy. This has to do with how stable the bonds are IN the molecule.

Boiling point only tells you how tightly the molecule “holds onto” other molecules of its kind. It is a physical, not a chemical, property. Boiling point is INTERmolecular, thermodynamic stability is INTRAmolecular.

The question is asking about the quality of the compounds themselves, so you shouldn’t be thinking about a property that requires more than one molecule (like boiling point).