Ch. 7: Thermochemistry

Question 1

Classification of Systems:
Isolated Systems
Closed Systems
Open Systems

Answer 1

Isolated: Exchange neither matter nor energy w the environment
Closed: Can exchange energy but not matter w the environment
Closed: Can exchange both energy and matter w the environment

Question 2

Characterization of process based on single constant property

Answer 2

Isothermal: occur at a constatnt temp
Adiabatic: exchange no heat w the environment
Isobaric: occur @ constant pressure
Isovolumetric (isochoric): occur at a constant volume

Question 3

State functions

Answer 3

Describe the physical properties of an equilibrium state; they are pathway independent and include pressure, density, temp, volume, enthalpy, internal energy, Gibbs free energy, and entropy

Question 4

Standard conditions

Answer 4

Defined as 298 K, 1 atm, and 1 M concentrations

Question 5

Standard State

Answer 5

Of an element is its most prevalent form under standard conditions
- Standard enthalpy, standard entropy, and standard free energy are all calculated under standard conditions

Question 6

Phase Changes:

Answer 6

Exist at characteristic temps and pressures

Question 7

Fusion and Freezing

Answer 7

Fusion (melting) and Freezing (crystallization or solidification) occur at the boundary between the solid and liquid phases

Question 8

Vaporization and Condensation

Answer 8

Vaporization (evaporation or boiling) and condensation occur at the boundary between the liquid and the gas phases

Question 9

Sublimation and Deposition

Answer 9

Occur at the boundary between solid and gas phases

Question 10

Critical Point

Answer 10

At temps above the critical point the liquid and gas phases are indistinguishable

Question 11

Triple Point

Answer 11

All three phases of matter exist in equilibrium

Question 12

Phase diagram

Answer 12

For a sys graphs the phases and phase equilibria as a function of temp and pressure

Question 13

Temperature

Answer 13

Scaled measure of avg kinetic energy of a substance

Question 14

Heat

Answer 14

Transfer of energy that results from differences of temp between two substances

Question 15

Heat content of a system

Answer 15

Undergoing heating cooling, or phase changes is the sum of all of the respective energy changes

Question 16

Enthalpy

Answer 16

Measure of the potential energy of a system found in intermolecular attractions and chemical bonds

Question 17

Hess’s law

Answer 17

States that the total change in potential energy of a system is equal to the changes of potential energies of the individual steps of the process

Question 18

Enthalpy calculation

Answer 18

Can be calculated using heats of formation, heats of combustion, or bond dissociation energies

Question 19

Entropy

Answer 19

Measure of the degree to which energy has been spread throughout a syste or between a system and its surroundings

• Ratio of heat transferred per mole per unit kelvin
• Maximized at equilibrium

Question 20

Gibbs Free Energy

Answer 20

Derived from both enthalpy and entropy values for a given system

Question 21

Change in Gibbs Free Energy

Answer 21

Determines whether a process is spontaneous or nonspontaneous
🔺G < 0; reaction proceeds in forward direction (spontaneous)
🔺G = 0; reaction is in dynamic equilibrium
🔺G > 0; reaction proceeds in reverse direction (nonspontaneous)

Question 22

Temperature Dependence

Answer 22

Gibbs free energy depends on temperature; temperature-dependent processes change between spontaneous or nonspontaneous, depending on the temp