The rate of reaction between magnesium ribbon and dilute hydrochloric acid at room temperature is investigated - Edexcel - GCSE Chemistry Combined Science - Question 6 - 2018 - Paper 1

To calculate the rate of reaction, determine the slope of the tangent at the chosen point. For a tangent, the calculation would involve determining the rise over run based on the coordinates of two points on the tangent line. If the tangent passes through points (15, 43) and (60, 60), the calculation would be:

$ext{Rate} = \frac{60 - 43}{60 - 15} = \frac{17}{45} \approx 0.38 \, \text{cm}^3/s$

The line should be steeper than the one for magnesium ribbon because powdered magnesium has a larger surface area for the reaction, which increases the rate of reaction.

To calculate the number of moles, use the formula:

$\text{Number of moles} = \frac{\text{mass}}{\text{molar mass}} = \frac{0.1 \, \text{g}}{24 \, \text{g/mol}} \approx 0.00417 \, \text{mol}$

The balanced equation is:

$\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2$

From the balanced equation, 1 mole of Mg reacts with 2 moles of HCl. Thus, for 0.5 moles of HCl, we require:

$0.5 \, \text{mol} \times \frac{1 \, \text{mol Mg}}{2 \, \text{mol HCl}} = 0.25 \, \text{mol of Mg}$

Since we have 0.5 mol of Mg, this shows that magnesium is in excess.

Increasing the temperature increases the kinetic energy of the particles, resulting in more frequent and more energetic collisions between the reactant molecules. This increases the rate of reaction.

Similarly, increasing the concentration of A increases the number of particles in a given volume, leading to more collisions between A and B molecules. This also results in a higher rate of reaction. Experiment 3 shows the most rapid reaction time due to the combined effects of increased temperature and higher concentration of A.