Thermodynamics

Question 1

What do ΔG and ΔG° represent in terms of spontaneity and standard conditions?

Answer 1

ΔG refers to the actual free energy change under specific conditions, while ΔG° refers to the free energy change under standard conditions.

Explanation: ΔG° is used as a reference point; spontaneity depends on ΔG.

Question 2

What is the relationship between ΔG and ΔG°?

Answer 2

ΔG = ΔG° + RT ln(Q), where Q is the reaction quotient.

Explanation: This accounts for non-standard concentrations or partial pressures.

Question 3

How are enthalpy (ΔH) and entropy (ΔS) related to free energy?

Answer 3

ΔG = ΔH - TΔS

Explanation: This equation shows how both enthalpy and entropy determine the spontaneity of a process.

Question 4

What does it mean for a reaction to be spontaneous?

Answer 4

It means ΔG is negative, indicating the process can proceed without input of energy.

Explanation: Negative ΔG implies a thermodynamically favorable reaction.

Question 5

How does entropy influence the spontaneity of a reaction?

Answer 5

An increase in entropy (ΔS > 0) generally makes ΔG more negative, favoring spontaneity.

Explanation: More disorder usually helps a reaction proceed.

Question 6

What is the formula connecting ΔG° and the equilibrium constant (K)?

Answer 6

ΔG° = -RT ln(K)

Explanation: This relates the standard free energy change to the equilibrium constant.

Question 7

Given ΔG°, how do you calculate K? And vice versa?

Answer 7

K = e^(-ΔG°/RT) and ΔG° = -RT ln(K)

Explanation: Rearranged versions of the same equation connecting thermodynamics and equilibrium.

Question 8

How do you calculate ΔG using ΔG° and non-equilibrium concentrations?

Answer 8

ΔG = ΔG° + RT ln(Q)

Explanation: This adjusts the standard free energy to actual conditions.

Question 9

What makes ATP a “high-energy” compound?

Answer 9

It has high-energy phosphoanhydride bonds that release energy when hydrolyzed.

Explanation: Hydrolysis of ATP is highly exergonic and drives cellular work.

Question 10

How do you calculate ΔG° for a coupled reaction?

Answer 10

Add the ΔG° values of the two individual reactions.

Explanation: Free energy changes are additive for sequential reactions.

Question 11

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Answer 11

Back

Question 12

What does ΔG indicate about a reaction?

Answer 12

ΔG indicates whether a reaction is spontaneous under current conditions. If ΔG < 0, the reaction is spontaneous.

Explanation: Spontaneous means it can occur without continuous energy input.

Question 13

What does ΔG° represent?

Answer 13

ΔG° represents the free energy change under standard conditions (1 M, 1 atm, 25°C, pH 7 for biochemistry).

Explanation: It’s a reference value used to calculate ΔG under non-standard conditions.

Question 14

How are ΔG and ΔG° related?

Answer 14

ΔG = ΔG° + RTlnQ

Explanation: This equation accounts for actual concentrations (Q) affecting spontaneity.

Question 15

What is the condition for equilibrium in terms of ΔG?

Answer 15

At equilibrium, ΔG = 0.

Explanation: The system is at its lowest free energy, and the forward and reverse rates are equal.

Question 16

What is the equation for free energy involving enthalpy and entropy?

Answer 16

ΔG = ΔH - TΔS

Explanation: ΔH is heat exchange, ΔS is energy dispersal; both influence spontaneity.

Question 17

What does a negative ΔH mean?

Answer 17

The reaction is exothermic and releases heat.

Explanation: This contributes favorably to spontaneity.

Question 18

What does a positive ΔS mean?

Answer 18

Energy is more dispersed, increasing disorder.

Explanation: This also favors spontaneity.

Question 19

When is a reaction with ΔH > 0 and ΔS > 0 spontaneous?

Answer 19

At high temperatures.

Explanation: TΔS becomes large and can outweigh ΔH.

Question 20

What is the effect of temperature on spontaneity for ΔH < 0 and ΔS < 0?

Answer 20

Reaction is spontaneous at low temperature.

Explanation: TΔS is small and doesn’t overwhelm negative ΔH.

Question 21

How is ΔG° related to the equilibrium constant K?

Answer 21

ΔG° = -RT ln K

Explanation: More negative ΔG° means larger K, favoring products.

Question 22

How can a reaction with ΔG° > 0 still be spontaneous?

Answer 22

If Q is small enough, then ΔG = ΔG° + RTlnQ < 0.

Explanation: Concentration effects can drive unfavorable reactions.

Question 23

What is a coupled reaction?

Answer 23

An unfavorable reaction paired with a favorable one to make the net ΔG negative.

Explanation: ATP hydrolysis often provides the favorable ΔG.

Question 24

Why is ATP a good energy currency?

Answer 24

It has an intermediate ΔG of hydrolysis and can drive many reactions.

Explanation: It’s high enough to be useful but not so high it’s uncontrollable.

Question 25

List reasons ATP hydrolysis is favorable.

Answer 25

Electrostatic repulsion, product stabilization via resonance, and entropy increase. Explanation: All these contribute to a large -ΔG.

Question 26

Calculate ΔG given ΔH = 6.03 kJ/mol and ΔS = 22.1 J/mol·K at 298 K.

Answer 26

ΔG = 6030 J - (298)(22.1) = -556 J/mol. Explanation: A spontaneous process (ΔG < 0).

Question 27

Given ΔG° = -30.5 kJ/mol at 37°C, calculate Keq.

Answer 27

K_eq = e^(-ΔG°/RT) = e^{(30500 / (8.314*310))} ≈ 5.1×10⁵ Explanation: Large Keq favors product formation.