WAEC Chemistry 2024 Paper

Concept:In gaseous reactions at the same temperature and pressure, gas volumes react in the same ratio as their mole coefficients in the balanced equation.Explanation:The balanced combustion equation is:$2\mathrm{C_2H_6(g)} + 7\mathrm{O_2(g)} \rightarrow 4\mathrm{CO_2(g)} + 6\mathrm{H_2O(g)}$Since oxygen is in excess, ethane is the limiting reactant, so its volume determines the volume of steam formed.From the equation, 2 volumes of ethane produce 6 volumes of steam.Given volume of ethane burned = $400\ \mathrm{cm^3}$.Let the volume of steam produced be $x$.Using the volume ratio:$\frac{2}{6} = \frac{400}{x}$So,$x = \frac{400 \times 6}{2}$$x = 1200\ \mathrm{cm^3}$Answer:The volume of steam produced is $1200\ \mathrm{cm^3}$, which corresponds to option D.