A student investigates the reaction between magnesium and dilute hydrochloric acid, HCl\text{HCl}HCl. The student adds a piece of magnesium ribbon to dilute hydrochloric acid in a conical flask, as shown in the diagram.
Magnesium chloride, MgCl2\text{MgCl}_2MgCl2, and hydrogen gas, H2\text{H}_2H2, are formed.
Write the balanced symbol equation for this reaction.
The student measures the time it takes for all the magnesium to react. This is the reaction time. The student conducts five experiments.
The student makes the following prediction: “The greater the volume of acid and the greater the mass of magnesium, the shorter the reaction time.”
Look at the student’s results:
| Experiment | Mass of magnesium used (g\text{g}g) | Volume of acid used (cm3\text{cm}^3cm3) | Concentration of acid (mol/dm3\text{mol/dm}^3mol/dm3) | Reaction time (s\text{s}s) |
|---|---|---|---|---|
| 1 | 0.15 | 25 | 0.5 | 60 |
| 2 | 0.15 | 50 | 0.5 | 60 |
| 3 | 0.15 | 50 | 1.0 | 30 |
| 4 | 0.30 | 25 | 0.5 | 60 |
| 5 | 0.30 | 50 | 1.0 | 30 |
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.