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It is really easy to plan an experiment to see how changing the temperature of a solution affects the rate of a chemical reaction... in fact, we could easily use one of the two reactions we have already seen on previous pages... calcium carbonate reacting with hydrochloric acid..... or magnesium reacting with hydrochloric acid.
BUT, there is a much more interesting experiment we can look at, which doesn't involve us measuring mass loss or a volume of gas....
Na2S2O3(aq) + 2HCl(aq) ---> 2NaCl(aq) + H2O(l) + S(s) + SO2(g)
Don't worry about the scary looking chemical equation! Na2S2O3 has the name 'sodium thiosulphate' and that is the solution we are going to change the temperature of before adding the hydrochloric acid (HCl(aq)).
Before the experiment starts, both the sodium thiosulphate and the hydrochloric acid are colourless liquids (they look just like water!) But once they mix and the reaction starts, sulphur starts being produced as one of the products. Because the sulphur is insoluble, it just floats around and makes the mixture go very cloudy!
If you place the conical flask on top of a piece of paper with a cross drawn on it, then you can time how long it takes for this cloudiness (formation of a precipitate) to block out the cross from sight.
Some example results are below...
It's clear from these results that as the temperature of the sodium thiosulphate increases, the time taken for the cross to disappear decreases. This means that the reaction happens faster at a higher temperature.
But why?
When the temperature is increased, the particles move faster AND they gain energy. This means that not only are there more frequent collisions in a given period of time, but each of the collisions occurs at a higher energy. So that means there will be a lot more successful collisions (that are above the activation energy).
In fact, changing the temperature has the largest effect on the rate. It is the only factor we can change that makes the particles gain energy!
As a general rule, an increase of just 10oC will make the rate of a reaction double!
INCREASING THE TEMPERATURE INCREASES THE RATE OF A CHEMICAL REACTION.
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