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R1.4 Entropy and spontaneity (HL) - IB Questionbank | RevisionDojo

Practice R1.4 Entropy and spontaneity (HL) with authentic IB Chemistry exam questions for both SL and HL students. This question bank mirrors Paper 1A, 1B, 2 structure, covering key topics like atomic structure, chemical reactions, and organic chemistry. Get instant solutions, detailed explanations, and build exam confidence with questions in the style of IB examiners.

Paper

Level

Question 1

HLPaper 2

Melting ice is a spontaneous process at room temperature.

Predict the sign of $\Delta S$ for the melting of ice.

[1]

State one reason for this prediction.

[1]

Explain in terms of particle arrangement why entropy increases during melting.

[2]

Question 2

HLPaper 2

Reaction: ${H_2(g) + I_2(g) \to 2HI(g)}$

$\Delta H^\circ = +26\ \mathrm{kJ\ mol^{-1}}$ ,

$\Delta S^\circ = +164\ \mathrm{J\ mol^{-1} K^{-1}}$

Calculate $\Delta G^\circ$ at $298\ \mathrm{K}$ .

[2]

Calculate temperature where $\Delta G^\circ = 0$ .

[2]

Question 3

HLPaper 2

Ammonia synthesis: $N_2(g) + 3H_2(g) \to 2NH_3(g)$

$\Delta H^\circ = -92\ \mathrm{kJ\ mol^{-1}}$ ,

$\Delta S^\circ = -198\ \mathrm{J\ mol^{-1} K^{-1}}$

Calculate $\Delta G^\circ$ at $298\ \mathrm{K}$ .

[3]

State whether the reaction is spontaneous.

[1]

Predict the effect of increasing temperature on spontaneity.

[1]

Question 4

HLPaper 2

For a chemical reaction, the Gibbs free energy under non-standard conditions is given by:

$\Delta G=\Delta G^\ominus+RT\ln{⁡Q}$

Where:

$\Delta G^\circ = -10\ \mathrm{kJ\ mol^{-1}}$

$T = 298\ \mathrm{K}$

$Q = 0.10$

$R = 8.314\ \mathrm{J\ mol^{-1} K^{-1}}$

Calculate the value of $\Delta G$ under these conditions.

[3]

Determine whether the reaction is spontaneous under these conditions.

[1]

Explain what happens to the value of $\Delta G$ as the value of $Q$ increases.

[1]

Question 5

HLPaper 2

A student investigates the enthalpy change when potassium chloride ( ${KCl}$ ) dissolves in water. They dissolve $2.00\ \mathrm{g}$ of ${KCl(s)}$ in $100.0\ \mathrm{g}$ of water and observe the temperature drop from $25.0^\circ\mathrm{C}$ to $22.5^\circ\mathrm{C}$ . The specific heat capacity of water is $4.18\ \mathrm{J\ g^{-1}\ ^\circ C^{-1}}$ and the molar mass of ${KCl}$ is $74.55\ \mathrm{g\ mol^{-1}}$ .

Calculate the heat absorbed by the water using $Q = mc\Delta T$ .

[2]

Calculate the number of moles of ${KCl}$ dissolved.

[1]

Determine the enthalpy change of solution for ${KCl}$ in $\mathrm{kJ\ mol^{-1}}$ . Include the sign.

[2]

State the physical meaning of the sign of your answer to Part 3.

[1]

Discuss why the dissolution of an ionic solid like ${KCl}$ can be spontaneous even when it is endothermic.

[2]

Question 6

HLPaper 2

Calcium carbonate decomposes on heating: ${CaCO_3(s) \to CaO(s) + CO_2(g)}$

Predict the sign of $\Delta S^\circ$ for this reaction.

[1]

Explain your answer in Part 1 using physical states.

[2]

Define entropy in terms of energy distribution.

[1]

Question 7

HLPaper 1A

Which change results in the largest negative value of $ΔS$ ?

Question 8

HLPaper 1A

The combustion of glucose is exothermic and occurs according to the following equation:

$C_6H_{12}O_6 (s) + 6O_2 (g) → 6CO_2 (g) + 6H_2O (g)$

Which is correct for this reaction?

Answer	ΔH°	ΔS°	Spontaneous / non-spontaneous
A	Negative	Positive	Spontaneous
B	Negative	Positive	Non-spontaneous
C	Positive	Negative	Spontaneous
D	Positive	Positive	Non-spontaneous

Question 9

HLPaper 1A

Which term in the expression $ΔG^\ominus = ΔH^\ominus − TΔS^\ominus$ is an indirect measure of the entropy change of the surroundings when divided by $T$ ?

Question 10

HLPaper 1A

Which statement is correct?

R1.4 Entropy and spontaneity (HL) Questionbank