Question 1a

Marks: 3

a)

State whether there is an increase or decrease in entropy for the following reactions.

i)

H₂O (l) → H₂O (g)

[1]

ii)

Cl₂ (g) → Cl₂(l)

[1]

iii)

CaCO₃ (s) → CaO (s) + CO₂ (g)

[1]

Key Concepts

Predicting Entropy Changes
Entropy

Question 1b

Marks: 1

b)

State the equation to determine the entropy change, ΔS , of a reaction.

[1]

Key Concepts

Calculating Standard Entropy Change

Question 1c

Marks: 1

c)

Use your answer to part b) and section 12 of the data booklet to determine the standard entropy change, in J K^-1 mol^-1 , for water boiling.

H₂O (l) → H₂O (g)

[1]

Key Concepts

Calculating Standard Entropy Change

Question 1d

Marks: 1

d)

Explain why the entropy change of the following precipitation reaction is negative.

AgNO₃ (aq) + NaCl (aq) → NaNO₃ (aq) + AgCl (s)

[1]

Key Concepts

Predicting Entropy Changes

Question 1e

Marks: 1

e)

State the point of a reversible reaction in which the Gibbs free energy is at its lowest.

[1]

Key Concepts

Free Energy & Equilibrium

Question 2a

Marks: 4

a)

Use section 12 of the data booklet and the information below to determine the following:

2NaHCO₃ (s) → Na₂CO₃ (s) + CO₂ (g) + H₂O (g)

Compound	ΔH_f(kJ mol^-1)
NaHCO₃ (s)	-951
Na₂CO₃ (s)	-1131

i)

The sum of the enthalpies of formation, ΔH_f , of the products in kJ mol^-1.

[1]

ii)

The sum of the enthalpies of formation, ΔH_f , of the reactants in kJ mol^-1.

[1]

iii)

Use your answers to part i) and ii) to determine the enthalpy change of reaction, ΔH_r, for the decomposition of sodium hydrogen carbonate, NaHCO₃ (s) in kJ mol^-1.

[2]

Key Concepts

Using ∆Hf° to find enthalpy changes

Question 2b

Marks: 4

b)

Use section 12 in the data booklet and the information below to determine the following:

2NaHCO₃ (s) → Na₂CO₃ (s) + CO₂ (g) + H₂O (g)

Compound	S(J K^-1 mol^-1)
NaHCO₃ (s)	+102
Na₂CO₃ (s)	+135

i)

The sum of the entropies, S , of the products in J K^-1 mol^-1

[1]

ii)

The sum of the entropies, S , of the reactants in J K^-1 mol^-1.

[1]

iii)

Use your answers to part i) and part ii) to determine the standard entropy change for the decomposition of sodium hydrogen carbonate, NaHCO₃(s), in J K^-1mol^-1.

[2]

Key Concepts

Calculating Standard Entropy Change

Question 2c

Marks: 2

c)

Use your answers to part a) and b) as well as section 1 in the data booklet to determine the free energy change, in kJ mol^-1 , for the decomposition of sodium hydrogen carbonate, NaHCO₃ (s), at 500 K.

[2]

Key Concepts

Gibbs Free Energy Change
Calculating ΔG° from the Gibbs Equation

Question 2d

Marks: 1

d)

Use your answer to part c) to state whether the decomposition of sodium hydrogen carbonate is spontaneous at 500K.

[1]

Key Concepts

Spontaneous Reactions

Question 3a

Marks: 1

a)

State the equation which can be used to determine the standard free energy for a reaction change, ΔG, using ΔG formation data.

[1]

Key Concepts

Calculating ΔG° from ΔG° Formation

Question 3b

Marks: 3

b)

Use section 12 of the data booklet and the equation below to determine the following.

C₃H₈ (g) + 5O₂ (g) → 3CO₂ (g) + 4H₂O (g)

i)

The sum of the Gibbs free enthalpy of formation, ΔG_f, of the products in kJ mol^-1.

[1]

ii)

The sum of the Gibbs free enthalpy of formation, ΔG_f, of the reactants, kJ mol^-1.

[1]

iii)

The Gibbs free energy change, ΔG , for the combustion of propane, kJ mol^-1.

[1]

Key Concepts

Calculating ΔG° from ΔG° Formation

Question 3c

Marks: 2

c)

The reaction of carbon monoxide with water is as follows:

CO (g) + H₂O (g) → CO₂ (g) + H₂ (g)

The entropy change, ΔS , for this reaction is -135 J K^-1 mol^-1 and the enthalpy change, ΔH , for the reaction is -41.4 kJ mol^-1.

Determine the free energy change, ΔG , for the reaction at 700 K in kJ mol^-1.

[2]

Key Concepts

Gibbs Free Energy Change

Question 3d

Marks: 1

d)

Use your answer to part b) state whether the reaction of carbon monoxide and water is spontaneous at 700 K.

[1]

Key Concepts

Spontaneous Reactions

Question 4a

Marks: 2

a)

The image below shows how the entropy of compound Y varies with temperature

2-1

State the changes occurring at T₁ and T₂.

[2]

Key Concepts

Entropy

Question 4b

Marks: 4

b)

Study the reaction of methane, CH₄ , with water shown.

CH₄ (g) + H₂O (g)

⇌

CO (g) + 3H₂ (g)

Use sections 12 and 13 of the data booklet to determine the following.

i)

The sum of the enthalpies of formation, ΔH_f , of the products in kJ mol^-1.

[1]

ii)

The sum of the enthalpies of formation, ΔH_f , of the reactants in kJ mol^-1.

[1]

iii)

Use your answers to part i) and ii) to determine the enthalpy change of reaction, ΔH_r, for the reaction kJ mol^-1.

[2]

Key Concepts

Using ∆Hf° to find enthalpy changes

Question 4c

Marks: 4

c)

The standard entropy of hydrogen gas is 131.0 J K^-1 mol^-1.

Use section 12 in the data booklet to determine the following for the reaction in part a).

i)

The sum of the entropies, S , of the products in J K^-1 mol^-1

[1]

ii)

The sum of the entropies, S , of the reactants in J K^-1 mol^-1.

[1]

iii)

Use your answers to part i) and part ii) to determine the reaction given in part a) in J K^-1 mol^-1.

[2]

Key Concepts

Calculating Standard Entropy Change

Question 4d

Marks: 3

d)

We can use the equation ΔG = ΔH - TΔS to determine the temperature, in K, at which a reaction becomes feasible.

Use your answers to part b) and c) as well as section 1 of the data booklet to determine the following.

The equation required to determine the temperature at which a reaction becomes spontaneous

..........................................................................................................................................................................

The temperature at which the reaction of methane, CH₄ , and water becomes spontaneous

..........................................................................................................................................................................

[3]

Key Concepts

Spontaneous Reactions
Gibbs Free Energy Change
Calculating ΔG° from the Gibbs Equation

DP IB Chemistry: HL

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15.2 Entropy & Spontaneity

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