IB Chemistry SL R1.1 Measuring enthalpy changes questions

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Question 1

Multiple choiceEasy1 mark

A reaction occurs in a flask immersed in water. The water temperature decreases during the reaction. Which description of the reaction is correct?

Show answer and explanation

Answer: D. The reaction is the system and the water is its surroundings. As the water cools, it loses energy to the reaction system. The reaction is therefore endothermic.

A: Reverses the temperature evidence; energy transferred to the water would warm it. B: Recognizes the endothermic classification but reverses the direction of energy transfer. C: Gives the transfer direction indicated by the cooling water but labels energy absorption by the system as exothermic.

Remember: cooling surroundings transfer energy to the system.

Question 2

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]

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