RP 3 - Effect of temperature on rate of a reaction

Question 1

How can rate of reaction be measured?

Answer 1

• Initial rates method - i.e the iodine clock reaction
• A continuous monitoring - method i.e measuring the volume of gas released in a reaction overtime

Question 2

Why does rate of reaction increase with increasing temperature?

Answer 2

• As temperature increases the kinetic energy of the molecules increases. This means more molecules have energy greater than the activation energy and can therefore react.
• Also as kinetic energy of molecules increases their velocity increase resulting in more frequent and successful collisions

Question 3

How would you investigate how the rate of reaction varies with temperature?

Answer 3

Na2S2O3(aq) + 2HCl(aq) -> 2NaCl(aq) + SO2(g) + S(g)

• This reaction produces a cloudy sulphur precipitate
• to measure rate time how long it takes for a cross underneath the beaker to disappear using a stopwatch
• Repeat this at five different temperatures and compare times taken

Question 4

What are some issues with the disappearing cross method?

Answer 4

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

Question 5

How could you analyse the data from the disappearing cross method?

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
• Therefore the gradient of this straight section = rate of reaction
• Compare the rate of reaction for each temperature for further analysis you could plot a graph of rate of reaction against temperature.

Question 6

What is a control variable?

Answer 6

A variable that is kept constant throughout the experiment

Question 7

In an experiment investigating the effective 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 constant temperature?

Answer 8

Using water bath keeps the temperature constant. For this experiment you can set up water baths of different temperatures to see how it affects the rate of reaction.