(a) State two factors which can affect the rate of a chemical reaction. (b) 0.72g of magnesium was added to different volumes of 2 mol. per dm\(^{3}\) hydro...

(a) Two factors which affect the rate of a chemical reaction are:

1. Concentration of the reactants.
2. Temperature of the reacting mixture.

(b) The graph is plotted with volume of 2 mol dm⁻³ HCl on the horizontal axis and volume of hydrogen evolved on the vertical axis.

(c) Reading from the graph:

1. For 50 cm³ of acid, the volume of hydrogen produced is 600 cm³.
2. The volume of acid required to produce 480 cm³ of hydrogen is approximately 21 cm³.
3. The volume of acid needed to dissolve the 0.72 g of magnesium completely is 35 cm³.

(d) At 35 cm³ of acid, the graph becomes horizontal at 600 cm³ of hydrogen. This shows that all the magnesium has been used up. Addition of more acid cannot produce more hydrogen because magnesium is now the limiting reactant.

(e)

1. Mass of magnesium used = 0.72 g.

   \[n(\mathrm{Mg})=\frac{0.72}{24}=0.030\ \text{mol}\]

   0.030 mol of Mg is completely dissolved by 35 cm³ of the acid.

   \[\text{Volume for 1 mol Mg}=\frac{35}{0.030}=1166.7\ \text{cm}^3\]

   Therefore, 1.17 × 10³ cm³ of the acid will dissolve 1 mole of magnesium completely.

2. 0.030 mol of Mg produces 600 cm³ of hydrogen.

   \[\text{Volume of }\mathrm{H_2}\text{ for 1 mol Mg}=\frac{600}{0.030}=2.00\times10^4\ \text{cm}^3\]

   Therefore, 2.00 × 10⁴ cm³ of hydrogen is liberated when 1 mole of magnesium dissolves completely.

3. The balanced equation is:

   \[\mathrm{Mg_{(s)}+2HCl_{(aq)}\rightarrow MgCl_{2(aq)}+H_{2(g)}}\]