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

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Question 1

Paper 2Medium4 marks

A student burns ethanol, C₂H₅OH, completely in oxygen to heat 200.0 g of water. The mass of ethanol consumed is 0.460 g, and the water temperature rises from 20.00 °C to 23.40 °C. The experiment is carried out at constant pressure.

Refer to the data booklet for the relative atomic masses and the specific heat capacity of water.

(a)

Determine the experimental molar enthalpy change of combustion of ethanol, in kJ mol⁻¹, to three significant figures.

[3]
(b)

Using the sign of your answer to (a), identify whether the reactants or the products are more stable.

[1]

Question 2

Paper 2Medium6 marks

Carbon monoxide can be formed by the incomplete combustion of graphite and can be oxidized further to carbon dioxide. At 298 K, the standard enthalpy changes for the following reactions are:

C(graphite, s) + O₂(g) → CO₂(g)  ΔH° = −393.5 kJ mol⁻¹

CO(g) + ½O₂(g) → CO₂(g)  ΔH° = −283.0 kJ mol⁻¹

(a)

Write a balanced equation, including state symbols, for the formation of exactly 1 mol of CO(g) from its elements in their standard states.

[1]
(b)

Construct an energy cycle using the information above and your equation in (a), then calculate the standard enthalpy change for the formation of CO(g). Give your answer in kJ mol⁻¹.

[3]
(c)

Using the sign of your answer in (b), explain what it indicates about the direction of energy transfer and the relative enthalpy of the products and reactants.

[2]

Question 3

Multiple choiceMedium1 mark

A sensor is powered by a hydrogen fuel cell supplied with hydrogen and oxygen. It ceases operating when its hydrogen supply is exhausted. Which paired description accounts for the energy conversion and distinguishes the cell from a primary cell?

Show answer and explanation

Answer: D. A fuel cell converts chemical energy directly to electrical energy. Its reactants are supplied continuously, whereas the reactants of a primary cell are contained within the cell.

A: incorrectly extends continuous external reactant supply to primary cells. B: inserts heat as an intermediate energy form; the reactant-supply distinction is correct. C: reverses the reactant arrangements of fuel cells and primary cells.

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