Rates Of Reaction Coursework Introduction

Or you could measure the time taken for some dramatic colour change to occur. You then change the concentration of one of the components of the reaction, keeping everything else constant - the concentrations of other reactants, the total volume of the solution and the temperature and so on.Then you find the time taken for the same event to take place with that new concentration.You could also use a special flask with a divided bottom, with the catalyst in one side, and the hydrogen peroxide solution in the other. If you use a 10 cm measuring cylinder, initially full of water, you can reasonably accurately record the time taken to collect a small fixed volume of gas.

Or you could measure the time taken for some dramatic colour change to occur. You then change the concentration of one of the components of the reaction, keeping everything else constant - the concentrations of other reactants, the total volume of the solution and the temperature and so on.

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That's because in a first order reaction, the rate is proportional to the concentration. It might be second order - but it could equally well have some sort of fractional order like 1.5 or 1.78.

The best way around this is to plot what is known as a "log graph".

Since this is the part of the reaction you are most interested in, introducing errors here would be stupid!

You have to find a way of adding the catalyst to the hydrogen peroxide solution without changing the volume of gas collected.

This is repeated for a range of concentrations of the substance you are interested in.

You would need to cover a reasonably wide range of concentrations, taking perhaps 5 or so different concentrations varying from the original one down to half of it or less.Obviously, you could then repeat the process by changing something else - the concentration of a different substance, or the temperature, for example.Understanding the results We will take a simple example of an initial rate experiment where you have a gas being produced.A measure of the rate of the reaction at any point is found by measuring the slope of the graph. Since we are interested in the initial rate, we would need the slope at the very beginning.If you then look at the second graph, enlarging the very beginning of the first curve, you will see that it is approximately a straight line at that point. I wouldn't really recommend that you try to read it all in one go.Or it could be the time taken for a small measurable amount of precipitate to be formed.If you added it to the flask using a spatula, and then quickly put the bung in, you might lose some gas before you got the bung in.Alternatively, as you pushed the bung in, you might force some air into the measuring cylinder. To start the reaction, you just need to shake the flask so that the weighing bottle falls over, and then continue shaking to make sure the catalyst mixes evenly with the solution.If you look at the expressions in the table above, you should recognise that the initial rate is inversely proportional to the time taken.In symbols: In experiments of this sort, you often just use 1/t as a measure of the initial rate without any further calculations.