Thermodynamics

Question 1

system and surroundings

Answer 1

system = section of universe under study (open, closed, and isolated)
surroundings = remainder of universe outside system

Question 2

extensive vs. intensive properties

Answer 2

extensive - change with amount, proportional to size of system (V and n)
intensive - do not change with amount, independent of size of system (P and T)

Question 3

state function

Answer 3

properties that describe the state of a system

• pathway independent
• change in a state property going from one state to another is the same regardless of the process used to change it

Question 4

path function

Answer 4

depend upon pathway used to achieve state (work and heat)

Question 5

2 ways to transfer energy between systems

Answer 5

heat (natural transfer of energy from a warmer body to a cooler body by conduction, convection, or radiation) and work

Question 6

conduction

Answer 6

thermal energy transfer via molecular collisions, requires direct physical contact

Question 7

convection

Answer 7

thermal energy transfer via fluid movements, differences in pressure or density drive warm fluid in the direction or cooler fluid

Question 8

radiation

Answer 8

thermal energy transfer via electromagnetic waves

Question 9

PV work

Answer 9

at constant pressure, it is equal to the product of the pressure and the change in volume
w = P(delta V) = work done by the gas
work done on the gas is (-)

Question 10

1st Law of Thermodynamics

Answer 10

energy of the system and surroundings is always conserved

delta E = q + w

Question 11

heat flow between two systems that _____ is an irreversible process

Answer 11

heat flow between 2 systems that are not at the same temperature is an irreversible process

Question 12

2nd Law of Thermodynamics

Answer 12

• work is required to transfer energy from a cold reservoir to a hot reservoir
• heat cannot be completely converted to work in a cyclical process
• the entropy of an isolated system will never decrease
• could be violated, but unlikely

Question 13

temperature

Answer 13

• measure of the thermal energy per mol of molecules
• thermodynamic property described by the zeroth law
• measurement of how fast the molecules are moving or vibrating
• Increase in thermal energy increases temperature

Question 14

the greater the random translational kinetic energy of gas molecules per volume, the great the ___

Answer 14

pressure

Question 15

enthalpy

Answer 15

not conserved like energy, enthalpy of the universe does not remain constant
*a state function (since U, P, and V are state functions)

Question 16

enthalpy and internal energy depend only on ___

Answer 16

temperature (enthalpy increase with temperature)

Question 17

change in enthalpy

Answer 17

delta H = delta U + P (delta V)

U is internal energy

Question 18

enthalpy change for only PV work at constant pressure

Answer 18

delta H = q (constant pressure, closed system at rest, PV work only)

Question 19

Standard state

Answer 19

scientists assigned enthalpy values to compounds based on their standard states

• the reference form of a substance at any chosen temperature and a pressure of 1 bar (about 750 torr, 105 Pa)
• assume 1 bar (1 atm)

Question 20

reference form

Answer 20

the from that is most stable at 1 bar and a given temperature

Question 21

standard enthalpy of formation

Answer 21

change in enthalpy for a reaction that creates one mole of that compound from its raw elements in their standard state.
-can be found by experiment

Question 22

heat of reaction

Answer 22

delta H reaction = standard enthalpy of formation of products - standard enthalpy of formation of reactants

Question 23

Hess’s law

Answer 23

the sum of the enthalpy changes for each step is equal to the total enthalpy change regardless of the path chosen (enthalpy is a state function)
-forward reaction has exactly the opposite change in enthalpy as the reverse

Question 24

endothermic

Answer 24

if enthalpy change is positive, heat flow to the system

Question 25

exothermic

Answer 25

if enthalpy change is negative, heat to surroundings

Question 26

transition state

Answer 26

old bonds breaking and new bonds forming, during reaction collision (not intermediates)
-at peak of activation energy hill

Question 27

catalyst and enthalpy change

Answer 27

catalyst does not affect enthalpy change

Question 28

knowing what delta H is - page 77

Answer 28

page 77

Question 29

entropy

Answer 29

S, nature’s tendency toward disorder, tendency to create the most probable situation that can occur within a system, spread energy evenly throughout the universe

• state function, extensive property
• dictates direction of a reaction

Question 30

2nd law of thermo. entropy

Answer 30

delta S system + delta S surroundings = delta S universe >= 0
*the of a system can decrease only if the entropy of the surroundings increases by a greater or equal magnitude

Question 31

3rd law of thermodynamics

Answer 31

conventionally assigns a zero entropy value to any pure substance at absolute zero and in internal equilibrium.
all other substances have a positive entropy value

Question 32

since entropy in an isolated system cannot decrease, the universal entropy change for any reversible reaction must be ____

Answer 32

must be zero in both directions

Question 33

equilibrium is point of ____ entropy

Answer 33

maximum universal entropy

Question 34

Gibbs free energy

Answer 34

delta G = delta H - T(delta S)

refers to changes in system

Question 35

delta G = 0

Answer 35

equilibrium

Question 36

negative delta G

Answer 36

spontaneous reaction