Chemistry 0620 · IGCSE · Exothermic and endothermic reactions

Exothermic and endothermic reactions — practice question

The balanced equation for the complete combustion of ethanol, $\text{C}_2\text{H}_5\text{OH}$, is given below. $\text{C}_2\text{H}_5\text{OH} + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 3\text{H}_2\text{O}$ When one mole of ethanol is completely burnt, 1280 kJ of energy is given out. A section of the energy level diagram for this reaction is shown.
(a)[3]

Finish the energy level diagram so that it shows the reaction products and the overall energy change for the reaction.

(b)[1]

What is represented by X?

(c)[4]

Use the bond energy values in the table to work out the energy change, $\Delta H$, for the complete combustion of one mole of methanol.

(d(i))[1]

Name the process taking place in stage 1.

(d(ii))[2]

Write a chemical equation for the reaction taking place in stage 1.

(d(iii))[2]

State two conditions needed for stage 2.

(d(iv))[1]

Name the type of reaction occurring in stage 2.

(d(v))[2]

Suggest a method for checking the purity of the ethanol produced.

(e(i))[2]

State two conditions needed for glucose fermentation.

(e(ii))[2]

Complete the chemical equation for glucose fermentation. $\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow \cdots\cdots \, \text{C}_2\text{H}_5\text{OH} + \cdots\cdots$

(e(iii))[1]

Suggest why the ethanol concentration obtained by fermentation does not rise above 15%.

(e(iv))[1]

Give one additional disadvantage of producing ethanol by fermentation.

(e(v))[1]

Give one advantage, apart from cost, of producing ethanol by fermentation.

(e(vi))[1]

Suggest the name of a process used to separate ethanol from a mixture of ethanol and water.

(f(i))[1]

Write the empirical formula of ethane-1,2-diol.

(f(ii))[1]

Explain why ethane-1,2-diol cannot undergo addition polymerisation.

(f(iii))[3]

Draw the condensation polymer produced from ethane-1,2-diol and molecule Y. Show one repeat unit. Show every atom and every bond in the linkage.

(f(iv))[1]

Name the type of condensation polymer made from ethane-1,2-diol and molecule Y.

Worked solution & mark scheme

This 30-mark question has a full step-by-step worked solution and mark scheme. One marking point: horizontal line showing the products at a lower energy than the reactants (exothermic indication)

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