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Energy from Fuels · Paper 2 — Free Chemistry SL Practice Questions

1MasterySAQ-SCombustion reactions and energy release7 marksPaper 2~11 min

Methanol (

\text{CH}_3\text{OH}

) is being considered as a cleaner-burning alternative fuel for cars. In a laboratory test,

0.640\,\text{g}

of methanol is burned completely in a bomb calorimeter containing

850\,\text{g}

of water. The combustion reaction is:

2\text{CH}_3\text{OH}(l) + 3\text{O}_2(g) \rightarrow 2\text{CO}_2(g) + 4\text{H}_2\text{O}(l)

The temperature of the water rises from

22.5\,°\text{C}

36.8\,°\text{C}

. The specific heat capacity of water is

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

. The molar mass of methanol is

32.05\,\text{g}\,\text{mol}^{-1}

. The standard enthalpy of combustion of methanol is

-726\,\text{kJ}\,\text{mol}^{-1}

(a)

State two conditions required for complete combustion of methanol. [2 marks]

(b)

Calculate the heat energy, in kJ, released by the combustion of the

0.640\,\text{g}

sample. [2 marks]

(c)

Using your answer to (b), determine the experimental molar enthalpy of combustion of methanol in

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

. Hence evaluate the reliability of this experiment by comparing your value with the standard value. [3 marks]

Solutions

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