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Rate of reaction 3 - temperature

If you were a chemical manufacturer you would certainly be interested in finding ways to increase the rate of production. One way is to do the reaction at a higher temperature, and in this experiment you can see what sort of effect temperature has.

We'll use a reaction that is easy to do in school. For example, adding hydrochloric acid to sodium thiosulfate solution starts a reaction which causes turns the solution cloudy. As in the diagram, you can see how fast this happens by measuring how much light passes through the mixture. We used a light sensor to measure the light level and did the reaction at different temperatures.

##### What we did

We measured out 50 cm3 of 0.05M sodium thiosulfate and 10 cm3 of 1M hydrochloric acid. We then placed them in a water bath till they reached various temperatures. We tried this at 70 degrees; 53 degrees; 43 degrees; and 32 degrees Celsius. When the chemicals were at the required temperature we mixed them and recorded how fast they turned cloudy.

Our results

These graphs of light level against time show how quickly the reactions occur.

You will find some of the questions easier if you put these results into your data logging software. Click here to find the results, then Open the file in your data logging program.

### Looking at the results

• We measured this reaction at four different temperatures. Label the graphs to show which graph line corresponds to these temperatures.
• Take readings from the graph to find out when each reaction stopped getting cloudy. Remembering the temperatures of each, is there a pattern in your results?
• Take readings from the graph to find out when each reaction started getting cloudy. Remembering the temperatures of each, is there a pattern in your results?
• Use a spreadsheet or graph drawing program to plot these time readings against temperature.
• What effect does temperature have upon the time the reaction a) takes to stop, b) takes to start?
• What should the chemical manufacturer do to increase the rate of chemical production? How will this affect the manufacturer's costs of production?

### Extra

• Somebody knocked the lamp before one of the experiments. How and why has this affected the readings?
• Use your data logging software to measure the gradients (or the average gradients) of each of your graph lines. You will need to think about and discuss how you will do this.
• Use a spreadsheet or graph drawing program to plot these gradients against temperature. (Ignore the minus sign for the gradient).
• What shape is this graph? Also what does this graph tell you about the effect of temperature on the rate of the reaction?

### What you can do

Try a similar experiment yourself, but this time do one or two extra experiments at cooler temperatures.

### Where to get help

For other ideas and clues, see the Rates of reaction 2 experiment.

Activities in this section adapted from The IT in Science book of Data logging and Control. © IT in Science and may be reproduced as needed for use within your school.

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