RP 3 - Effect of Temperature on a Rate of Reaction

Question 1

How can rate of a reaction be measured?

Answer 1

• Initial rates method (iodine clock reaction)
• A continuous monitoring method (measure the volume of gas released over time)

Question 2

Why does the rate of reaction increase with temperature increase?

Answer 2

As temperature increases the kinetic energy of the molecules increase so their velocities increase so more frequent successful collisions so more molecules have energy greater than the activation energy so can react

Question 3

How would you investigate how the following rate of reaction increases with temperature?
Na2S2O3 + 2HCl -> 2NaCl + SO2 + S

Answer 3

This reaction produces a cloudy sulfur precipitate so to measure rate, time how long it takes for the cross underneath the beaker to disappear, using a stopwatch. As more sulfur is produced the harder it will be to see the cross. Repeat this at 5+ different temperatures and compare time taken

Question 4

What are some issues with the rates of reactions method using the disappearing cross?

Answer 4

• The disappeared cross is judged by eye so can be unreliable
• There may be a delayed reaction time with the stopwatch
• At low temperatures the reaction might be too slow
• There may not be enough precipitate produced for the cross to disappear

Question 5

With the rates of reactions method using the disappearing cross, how could you analyse the data?

Answer 5

For a graph of the amount of sulphur against time, it would be a straight line at the beginning as the reaction has only just begun so the gradient of this straight section is rate of reaction. Compare the rate of reaction for each temperature and for further analysis a graph of rate of reaction against time can be plotted

Question 6

What’s a control variable?

Answer 6

A variable that’s kept constant throughout the experiment

Question 7

In an experiment investigating the effect of temperature on rate of reaction, what variables will you control?

Answer 7

• Concentrations of reactants and products
• Volumes of reactants and products
• Use the same beaker and cross underneath
• Use the same person to decide when the cross has disappeared

Question 8

How can we keep a substance at a constant temperature?

Answer 8

Using a water bath