8 Thermodynamics

Question 1

The First Law of Thermodynamics

Energy can be

Answer 1

neither created nor destroyed

Question 2

The Second Law of Thermodynamics

If a process i spontaneous in one direction, then it can’t be spontaneous in

Answer 2

the reverse direction, and that entropy of the universe always increases during spontaneous reactions.

Question 3

Enthalpy change {Delta}H, entropy change {Delta}S, and free-energy change {Delta}G are state functions. This means that they all depend on the change that occurs

Answer 3

between the initial and the final states of a system, not on the process by which the change occurs.

Question 4

Standard State Conditions(6)

Denoted by the º superscript as in {Delta}Hº

Answer 4

• All gases are at 1 atm pressure
• All liquids are pure
• All solids are pure
• All solutions are at 1-molar (1 M) concentration
• The energy of formation of an element in its normal state is defined as zero
• The temperature used for standard state values is almost invariably room temperatuer: 25º C (298 K)

Question 5

The Basic Rules of Enthalpy

When bonds are formed, energy is

Answer 5

released.

When bonds are broken energy is absorbed

Question 6

Enthalpy Change {Delta}H =

Answer 6

H_products - Hreactants

Question 7

If the products have stronger bonds than the reactants, then

Answer 7

energy is released by the reaction, or the reaction is exothermic.

Question 8

If the products have weaker bonds than the reactants, then energy is

Answer 8

absorbed by the reaction, or the reaction is endothermic

Question 9

If {Delta}Hº_f for a compound is negative, energy is released when the compound is formed from pure elements, and the product is more stable than its constituent elements.

Answer 9

That is the process is exothermic.

Question 10

If {Delta}Hº_f for a compound is positive, energy is absorbed when the compound is formed from pure elements, and the product is less stable than its constituent elements.

Answer 10

That is the process is endothermic.

Question 11

{Delta}Hº =

Answer 11

(Sum) Bond energies of bonds broken - (Sum) bond energies of bonds formed.

Question 12

Hess’s Law

If a reaction can be described as a series of steps, then

Answer 12

{Delta}H for the overall reaction is siimply the sum of the {Delta}H values for all the steps.

Question 13

C_p =

Answer 13

{Delta}H / {Delta} T

C_p = Heat capacity

{Delta}H = heat added (J or Cal)

{Delta}T = temperature change (K or ºC)

Question 14

Specific heat is

Answer 14

the amount of heat required to raise the temperature of one gram of a substance one degree Celsius

Question 15

Specific Heat

q =

Answer 15

mc{Delta}T

q = heat added (J or cal)

m = mass of the substance (g or Kg)

c = specific heat

{Delta}T = temperature Change (K or Degrees C)

Question 16

The entropy, S, is

Answer 16

the measure of the disorder of the system; the greater the disorder the greater the entropy.

Question 17

Liquids have higher entropy values than

Answer 17

solids

Question 18

Gases have higher entropy values than

Answer 18

liquids

Question 19

Particles in solution have higher entropy values than

Answer 19

solids

Question 20

Two moles of a substance have higher entropy value than

Answer 20

one mole

Question 21

{Delta}Sº =

Answer 21

(Sum) {Delta}Sº_products - (Sum){Delta}Sº_reactants

Question 22

The Gibbs Free Energy, or simply free energy, G, of a process is

Answer 22

a measure of the spontaneity of the process.

Question 23

If {Delta}G is negative

Answer 23

the reaction is spontaneous.

Question 24

If {Delta}G is positive,

Answer 24

the reaction is not spontaneous

Question 25

If {Delta} G = 0,

Answer 25

the reaction is at equilibrium.

Question 26

{Delta}Gº =

Answer 26

(Sum) {Delta}Gºf products - (Sum) {Delta}Gºf reactants

Question 27

{Delta}Gº, {Delta}Hº, and {Delta}Sº

{Delta}Gº =

Answer 27

{Delta}Hº - T{Delta}Sº

Question 28

{Delta}H = -

{Delta}S = +

Temperture High or Low

Answer 28

{Delta}G = -

(Always spontaneous)

Question 29

{Delta}H = +

{Delta}S = -

Temperature high or low

Answer 29

{Delta}G = +

(Never spontaneous)

Question 30

{Delta}H = +

{Delta}S = +

Temperature Low

Answer 30

{Delta}G = +

(Not spontaneous at low temperature)

Temperature high

{Delta}G = -

(Spontaneous at high temperature)

Question 31

{Delta}H = -

{Delta}S = -

Temperature low

Answer 31

{Delta}G = -

(Spontaneous at low temperature)

Temperature high

{Delta}G = +

(Not spontaneous at high temperature)

Question 32

A Catalyst lowers the

Answer 32

activation energy.

Question 33

Activated Complex =

Answer 33

peak of graph

Question 34

The heat of vaporization is the heat given off when a substance

Answer 34

condenses. It is also the heat that must be put into a substance to make it vaporize.

Question 35

The heat of fusion is the heat that must be put into a substance

Answer 35

to melt it. It is also the heat given off when a substance freezes.

Question 36

The Third Law of Thermodynamics

The entropy of a perfect crystal at absolute zero

Answer 36

is exactly equal to zero.