IB Chemistry HL Reactivity 1: What drives chemical reactions? questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

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Question 1

Multiple choiceEasy1 mark

The figure shows the alcohol burned in a calorimetry experiment. A 0.230 g sample is combusted at constant pressure, warming 100.0 g of water from 20.0 °C to 26.0 °C. For the estimate, use the heat gained by the water as the heat released by combustion. The specific heat capacity of water is 4.18 J g⁻¹ K⁻¹. What molar enthalpy change of combustion is obtained, in kJ mol⁻¹?

CH₃CH₂OH
Show answer and explanation

Answer: A. The structure gives the formula C₂H₆O, so its molar mass is 46.07 g mol⁻¹. The water gains Q = mcΔT = 100.0 × 4.18 × 6.0 = 2508 J = 2.508 kJ. The amount of ethanol is 0.230/46.07 = 0.00499 mol, giving ΔH = −2.508/0.00499 = −502 kJ mol⁻¹.

B: uses the molar mass of CO₂, 44.0 g mol⁻¹, instead of ethanol’s. C: doubles the ethanol amount by applying the coefficient 2 for CO₂ to the fuel amount. D: reverses the sign, treating heat gained by the water as a positive enthalpy change for combustion.

Remember: heat released by an exothermic reaction gives a negative enthalpy change.

Question 2

Multiple choiceEasy1 mark

A reaction takes place in a vessel immersed in a water bath. The bath cools as the reaction proceeds. Which description of the reaction is correct?

Show answer and explanation

Answer: C. As the bath cools, it loses energy to the reaction. Energy transferred from the surroundings to the reaction makes the reaction endothermic.

A: identifies the reaction as endothermic but reverses the direction of energy transfer.
B: gives the correct direction of transfer but labels energy absorbed by the reaction as exothermic.
D: treats the bath’s cooling as evidence that the reaction releases energy, reversing the transfer direction and classification.
Remember: an endothermic reaction takes in energy from its surroundings.

Question 3

Paper 2Easy4 marks

Ethanol, C₂H₅OH(l), is used as a fuel. Its complete combustion produces carbon dioxide and liquid water. The standard enthalpies of formation at 298 K are:

SubstanceΔH°f / kJ mol⁻¹
C₂H₅OH(l)−277.7
O₂(g)0
CO₂(g)−393.5
H₂O(l)−285.8
(a)

Write the balanced equation for the complete combustion of ethanol, including state symbols.

[2]
(b)

Using the equation in (a) and the equation for enthalpies of formation in the data booklet, determine the standard enthalpy change for the combustion of 1 mol of ethanol. Give your answer in kJ mol⁻¹.

[2]

Question 4

Paper 2Easy8 marks

A student compares the air supply to two identical burners, each supplied with methane, CH₄, at the same rate. Figure 1 is a schematic diagram; the side arrows indicate the relative air supply to each burner.

ABCH4CH4
(a)

Using Figure 1, identify which burner is more likely to undergo incomplete combustion. Give one reason based on the figure.

[2]
(b)

For burner B, write a balanced equation for incomplete combustion of methane in which carbon monoxide and water are the products. State symbols are not required.

[2]
(c)

Ethanol, C₂H₅OH, burns with a restricted oxygen supply to form solid carbon and water. Write a balanced equation for this reaction. State symbols are not required.

[2]
(d)

State one health risk of carbon monoxide and suggest one change that would reduce the likelihood of carbon monoxide forming or accumulating.

[2]

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