WAEC Chemistry 2024 Paper

Concept:To find the coefficients $x$, $y$ and $z$, balance the chemical equation so that the number of atoms of each element is the same on both sides.Explanation:The reaction is written as:$$x\,\mathrm{Al} + y\,\mathrm{Cl}_2 \rightarrow z\,\mathrm{AlCl}_3$$Balance aluminium atoms:There is $x$ atom of $\mathrm{Al}$ on the left and $z$ atoms of $\mathrm{Al}$ in $\mathrm{AlCl}_3$.So, $x = z$.Balance chlorine atoms:On the left, each $\mathrm{Cl}_2$ molecule gives $2$ chlorine atoms, so there are $2y$ chlorine atoms.On the right, each $\mathrm{AlCl}_3$ has $3$ chlorine atoms, so there are $3z$ chlorine atoms.Thus, $2y = 3z$.Choose the smallest whole numbers.Let $z = 2$. Then $x = 2$.Now, $2y = 3(2) = 6$, so $y = 3$.The balanced equation is:$$2\,\mathrm{Al} + 3\,\mathrm{Cl}_2 \rightarrow 2\,\mathrm{AlCl}_3$$Therefore, $x = 2$, $y = 3$ and $z = 2$.Answer:The values of $x$, $y$ and $z$ are $2$, $3$ and $2$ respectively.Correct option: A.