Measuring rates of reaction
- Reactions take place at different rates depending on the chemicals involved and the conditions
- Some are extremely slow e.g. rusting and others are extremely fast e.g. explosives
- You should be able to describe experiments to investigate the effect of surface area, concentration, temperature and a catalyst on a rate of reaction
Effect of surface area of a solid on the rate of reaction
The process of downwards displacement to investigate the effect of the surface area of a solid on the rate of reaction
Method:
- Add dilute hydrochloric acid to the conical flask
- Use a delivery tube to connect this flask to an inverted measuring cylinder upside down in a water trough
- Add calcium carbonate chips into the conical flask and close the bung
- Measure the volume of gas produced in a fixed time using the measuring cylinder
- Repeat with different sizes of calcium carbonate chips
Result:
- With an increase in the surface area of the solid reactant, the rate of reaction will increase
- This is because there will be more of the solid reactant particles available for reaction, allowing more frequent and successful collisions, increasing the rate of reaction
Effect of concentration of a solution on the rate of reaction
The apparatus needed to investigate the effect of concentration on the rate of reaction
Method:
- Measure 50 cm3 of sodium thiosulfate solution into a flask
- Measure 5 cm3 of dilute hydrochloric acid into a measuring cylinder
- Draw a cross on a piece of paper and put it underneath the flask
- Add the acid into the flask and immediately start the stopwatch
- Look down at the cross from above and stop the stopwatch when the cross can no longer be seen
- Repeat using different concentrations of sodium thiosulfate solution (mix different volumes of sodium thiosulfate solution with water to dilute it)
Result:
- With an increase in the concentration of a solution, the rate of reaction will increase
- This is because there will be more reactant particles in a given volume, allowing more frequent and successful collisions, increasing the rate of reaction
Effect of temperature on the rate of reaction
Diagram showing the apparatus needed to investigate the effect of temperature on the rate of reaction
Method:
- Dilute hydrochloric acid is heated to a set temperature using a water bath
- Add the dilute hydrochloric acid into a conical flask
- Add a strip of magnesium and start the stopwatch
- Stop the time when the magnesium fully dissolves
- Repeat at different temperatures and compare results
Result:
- With an increase in the temperature, the rate of reaction will increase
- This is because the particles will have more kinetic energy than the required activation energy, therefore more frequent and successful collisions will occur, increasing the rate of reaction
Effect of a catalyst on the rate of reaction
Diagram showing the apparatus needed to investigate the effect of a catalyst on the rate of reaction
Method:
- Add hydrogen peroxide into a conical flask
- Use a delivery tube to connect this flask to a measuring cylinder upside down in water trough
- Add the catalyst manganese(IV) oxide into the conical flask and close the bung
- Measure the volume of gas produced in a fixed time using the measuring cylinder
- Repeat experiment without the catalyst of manganese(IV) oxide and compare results