In order for the particles to react with each other, they need a minimum amount of energy. This is known as the activation energy. If the colliding particles have less than the activation energy, the particles just bounce off each other and no reaction occurs.
When you increase the temperature, the particles gain energy and move around more. This means that they are more likely to collide with another particle and allow the chemical reaction to occur. The fact that there are more collisions taking place in the same amount time, it means that the rate of reaction will have increased.
Another reason why, as the temperature is increased, the rate of reaction will increase, is because as the particles gain energy they move around faster and so, they collide with more force. This means that a greater proportion of the particles will have the activation energy and so they will be able to collide successfully, causing the rate of reaction to increase.
In order to do my experiment I will need the following equipment:
- Sodium thiosulphate solution (200cm³)
- Hydrochloric acid (200cm³)
- Water (unlimited supply)
- Ice
- Test tubes (x10)
- 250ml beaker (x3)
- Thermometer
- Measuring cylinder
- Pipette
- Safety glasses
- Tongs
- Bunsen burner
- Matches
- Gauze
- Tripod
- Heatproof mat
- Whiteboard pen
- Stopwatch
Method
- Collect all the equipment.
- Put on your safety glasses.
- Measure out 200cm³ of sodium thiosulphate into a beaker and mark on the beaker ‘Sodium thiosulphate’ with the whiteboard pen.
(This is so that you do not get it mixed with the hydrochloric acid.)
- Now measure out 200cm³ of hydrochloric acid into a beaker and again, with the whiteboard pen mark the beaker, this time with ‘Hydrochloric acid.’
- Put some water into the third beaker and place it on the tripod, with the gauze to heat (using a bunsen burner), put the thermometer inside the water so that you can regularly check the temperature.
- As the water is heating, measure 5cm³ sodium thiosulphate, using a pipette and put it into a test tube.
- Repeat step 5 until you have filled 10 test tubes.
- On each of the 10 test tubes put a cross towards the bottom.
- Once the water is at 100°C place the first test tube in, stop heating the water and add 5cm³ of hydrochloric acid (measured with a pipette and put into a measuring cylinder) into the test tube with sodium thiosulphate. You must make sure that the cross is on the side of the test tube which is not facing you.
- As soon as you have added the hydrochloric acid, start the stopwatch immediately.
- Stop the stopwatch as soon as you cannot see the cross and record the time on a table of results.
- Take the test tube out of the beaker using the tongs.
- Repeat steps 8-11 but with replacing the temperature of 100°C to the following, 90°C, 80°C, 70°C, 60°C, 50°C, 40°C, 30°C, 20°C and 10°C.
When repeating the steps for 10°C you will need to use ice.
- Then repeat steps 5-13 twice to produce three sets of results.
- Once you have completed this put all the equipment away, if necessary wait for the equipment to cool before putting it into the cupboard.
My preliminary results show that my method, my chosen temperatures and the amount of hydrochloric acid and sodium thiosulphate is sufficient and will provide accurate, reliable results.
In order to keep my test fair, I will use the same hydrochloric acid and the same sodium thiosulphate. I will use the same amount of both the hydrochloric acid and sodium thiosulphate and I will not use a catalyst.
Analysis
My graph shows that as the temperature increases, the time taken for the sodium thiosulphate to react with the hydrochloric acid decreases. This, therefore, agrees with my prediction, that as the temperature increases, the rate of reaction also increases.
The trend of my graph is a negative curve. It is negative because at 10°C there is less energy than at 100°C, so there are fewer collisions and these collisions are with less force. It is a curve because as the temperature increases the reaction can only go so fast, and there is a limited amount of sodium thiosulphate and hydrochloric acid.