A student investigates the reaction between zinc and dilute hydrochloric acid, HCl\text{HCl}HCl. The student adds zinc ribbon to dilute hydrochloric acid in a beaker, as shown in the diagram. 
Zinc chloride, ZnCl2\text{ZnCl}_2ZnCl2, and hydrogen gas, H2\text{H}_2H2, are made.
Write the balanced symbol equation for this reaction.
The student measures the time it takes for all the zinc to react. This is the reaction time. The student does five experiments. This is the student’s prediction: “The larger the volume of acid and the larger the mass of zinc, the shorter the reaction time.” Look at the student’s results.
| Experiment | Mass of zinc used (g) | Volume of acid used (cm3\text{cm}^3cm3) | Concentration of acid (mol/dm3\text{mol/dm}^3mol/dm3) | Reaction time (s) |
|---|---|---|---|---|
| 1 | 0.10 | 20 | 1.0 | 40 |
| 2 | 0.10 | 40 | 1.0 | 40 |
| 3 | 0.10 | 40 | 2.0 | 20 |
| 4 | 0.20 | 20 | 1.0 | 40 |
| 5 | 0.20 | 40 | 2.0 | 20 |
Describe and explain whether the student’s results support their prediction. Include ideas about the reacting particle model in your answer.
The student repeats experiment 1. This time they use acid at a higher temperature. Explain, using the reacting particle model, what happens to the rate of reaction and predict the reaction time for this reaction.
During chemical reactions, reactants are used up and the rate of reaction decreases. Explain, in terms of particles, why the rate of reaction decreases.