Thermodynamics 3

Question 1

Describe a spontaneous reaction when it has a high activation energy.

Answer 1

Occurs slowly

Question 2

What is entropy a measure of?

Answer 2

• Randomness or disorder of a system.
• increase in order = decrease in entropy
• increase in disorder = increase in entropy

Question 3

How do we calculate change in entropy?

Answer 3

Final entropy - initial entropy

• If the change from initial to final results in an increase in randomness then Sfinal>Sinitial, thus, ΔS > 0

Question 4

What is the Second Law of Thermodynamics?

Answer 4

The entropy of an isolated system tends to increase.

Question 5

How to calculate a change in entropy of a substance?

Answer 5

The heart transferred reversibly to it divided by the temp. at which the transfer takes place.

Question 6

What does it mean that entropy is a state function?

Answer 6

its value only depends upon the present state of the system.

Question 7

Why reversible?

Answer 7

Equal temp. either side of a thermally conducting wall - no ‘hot spots’ and these would tend to spontaneously disperse and add to the entropy.

Question 8

Why heat not work?

Answer 8

Heat - random molecular motion whereas work is ordered molecular motion

Question 9

What does temperature got to do with entropy?

Answer 9

A given entropy change is more significant for a cold system than a hot one

Question 10

Give the equation for entropy changes accompanying heating.

Answer 10

ΔS = C ln (Tf/Ti)

Question 11

What does the equation ΔS = C ln (Tf/Ti) tell us?

Answer 11

That entropy changes are higher for materials with high heat capacities - more energy is required to cause a change in temp. for these materials.

Question 12

What is entropy and second law?

Answer 12

The amount of heat passing to/from the surroundings is equal and opposite to the heat leaving/entering the system.
Therefore, ΔSsur = -q/T

Question 13

At constant pressure wha does q equal?

Answer 13

q = ΔH therefore, ΔSsur = -ΔH/T

Question 14

Describe entropy for an exothermic reaction?

Answer 14

The surrounding gains heat and its entropy increases

Question 15

Describe entropy for an endothermic reaction?

Answer 15

The surrounding loses heat and entropy decreases.

Question 16

Define first law of thermodynamics.

Answer 16

Energy can be converted
from one form to another, but energy cannot be created or destroyed.

Question 17

Define the second law of thermodynamics.

Answer 17

The entropy of the
universe increases in a spontaneous process and remains unchanged in an equilibrium process.

Question 18

State the equation for entropy and probability.

Answer 18

S = k ln W
K = 1.38 x 10^-23 J/K
W = the number of way that the state can be achieved

Question 19

What is this third law of thermodynamics?

Answer 19

The entropy of a perfectly ordered crystalline substance at absolute zero

Question 20

Describe entropy at higher temp.

Answer 20

• Greater molecular motion
• Broader distribution of individual molecular energies
• More randomness
• Higher entropy

Question 21

Describe entropy at lower temperature.

Answer 21

• Less molecular motion
• Narrower distribution of individual molecular energies
• Less randomness
• Lower entropy

Question 22

Define state function?

Answer 22

A function or property whose value depends only on the present state, or condition, of the system, not on the path used to arrive at that state.

Question 23

How to calculate the standard entropy of a reaction?

Answer 23

ΔS^0rxn = ΣnS0(products) - ΣmS0(reactants)

Question 24

Describe spontaneity and the entropy of the universe.

Answer 24

Processes occur spontaneously if the overall entropy of the universe is increased.

Question 25

How do we calculate ΔSuniv?

Answer 25

ΔSuniv = ΔSsys + ΔSsur
ΔSsur = -ΔH/T, therefore, ΔSuniv = ΔSsys - ΔH/T

Question 26

How to calculate Gibbs ‘free’ energy (G)

Answer 26

ΔG = ΔH – TΔS

Question 27

Describe the reaction when ΔG< 0

Answer 27

The reaction is spontaneous in the forward direction.

Question 28

Describe the reaction when ΔG> 0

Answer 28

The reaction is nonspontaneous as written. The reaction is spontaneous in the reverse direction.

Question 29

Describe the reaction when ΔG= 0

Answer 29

The reaction is at equilibrium.

Question 30

How does Work relate to Gibbs Energy Change?

Answer 30

The ΔG of any process is the maximum non-expansion
work that can be extracted from that process at constant temperature and pressure.
Thus, ΔG = Wmax

Question 31

How to calculate standard free energies of formation?

Answer 31

G ° = G°f (products) - G°f (reactants)

Question 32

Give the equation for free energy changes and equilibria.

Answer 32

ΔG= ΔG° + RT lnK

Question 33

Describe the total free energy when the reaction mixture is mostly reactants.

Answer 33

The total free energy decreases as the reaction
proceeds spontaneously in the forward direction.

Question 34

Describe the total free energy when the reaction mixture is mostly products.

Answer 34

The total free energy decreases as the reaction
proceeds spontaneously in the reverse direction.

Question 35

Define a ligand.

Answer 35

• Any molecule that binds to
  another molecule.
• In common biochemical terminology “ligand”
  refers to a small molecule binding to a macromolecule.