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Measuring Enthalpy Change · Paper 2 — Free Chemistry SL Practice Questions

1ChallengeSAQ-LEnthalpy of reaction, heat capacity, and calorimetry6 marksPaper 2~9 min

A student carries out a calorimetry experiment to determine the enthalpy change for the combustion of propan-1-ol,

\text{C}_3\text{H}_7\text{OH(l)}

. A spirit burner heats

200.0\,\text{g}

of water in a copper calorimeter of mass

50.0\,\text{g}

(including stirrer). The initial temperature of the water is

21.5\,°\text{C}

and the final temperature is

35.2\,°\text{C}

. The mass of propan-1-ol burned is

0.420\,\text{g}

. The specific heat capacity of water is

4.18\,\text{J g}^{-1}\text{K}^{-1}

and the specific heat capacity of copper is

0.385\,\text{J g}^{-1}\text{K}^{-1}

. The student assumes all heat released by combustion is absorbed by the water and calorimeter.

(a)

Calculate the heat absorbed by the water and copper calorimeter, in J. [1 mark]

(b)

Calculate the amount, in mol, of propan-1-ol burned. [1 mark]

(c)

Determine the experimental enthalpy change of combustion of propan-1-ol, in

\text{kJ mol}^{-1}

. [2 marks]

(d)

Explain two reasons why the experimental value obtained in (c) is less exothermic than the literature value of

-2021\,\text{kJ mol}^{-1}

. [2] (e) The student notices the wick of the spirit burner continues to absorb propan-1-ol after the flame is extinguished, causing the recorded mass loss to be greater than the mass actually burned. - Identify the type of error this represents and state its effect on the calculated enthalpy change of combustion. - Suggest one specific modification to the experimental procedure that would eliminate this error. [2 marks]

Solutions

Questions 2-62

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