# To study how concentration affects the rate of a reaction.

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The Collision Theory

For particles to react, they must collide. They must also collide with enough energy for a reaction to take place. The energy created is called activation energy. The more often and faster the chemicals collide, the stronger the reaction.

Rate of Reaction

The rate of a reaction depends on four things:

*Temperature - When the temperature increases the particles start to all move quicker. This means that there will be more collisions and more energy will be given out.

*Concentration - If a solution is highly concentrated it means that there are a lot of particles that can collide. This means that there is more chance that a reaction will occur.

*Catalyst - A catalyst gives the reacting particles a surface to stick to and still collide. This lowers the activation energy, making it easier for the reaction to take place. A catalyst does not take place in the reaction itself.

*Size of particles (surface area) - A few small fragments of a substance will have a larger surface area than one large piece because the fragments will have more area for the solution to work on.

There are three ways you can measure the speed of a reaction.

*Precipitation - This is when the product of the reaction is a precipitate which clouds the solution

*Change in mass - If the reaction produces a gas, the experiment can be carried out on a mass balance. As the gas is released, the change in mass can be measured easily.

*Volume of gas given off - As gas is given out, a gas syringe measures the total amount released

Experiment write up

Aim

To plan and carry out an investigation that shows how concentration affects the rate of a reaction.

Key factors

I will only change the concentration of the acid while conducting this experiment. I will increase the concentration of the acid by 0.5 molar on each occasion.

Prediction

I predict that the reaction will become more rapid as the concentration of the hydrochloric acid increases. I think this because, as earlier stated, when the acid is highly concentrated there is more change of a reaction occurring. Therefore, a reaction with a 2.5 molar of hydrochloric acid will be a lot stronger than a reaction with a 0.5 molar.

I also think that the reactions with the weaker acids could in the end produce more hydrogen. The last couple of reactions will be very fast to start off with but will then die down very quickly. The first few reactions will be slower but will last a lot longer and could produce more hydrogen before the reaction fully comes to an end.

Method

First we gathered all the equipment needed and set it up as required. Then we measured out 20cm" of 0.5 molar hydrochloric acid. We then put a 8cm long magnesium strip inside a conical flask, added the acid and inserted the gas syringe into the top of flask. We then started timing and every 10 seconds we took readings from the gas syringe until the reaction had come to a halt. We recorded the results and then carried out the same experiment another two times. We did this to ensure that our test was fair and that we got the correct results. We repeated these steps until we had results for all concentrations of hydrochloric acid up to and including 2.5 molar.

Fair test

I will keep the following things the same each time to ensure that the test is fair:

*The length of the magnesium strip (8cm)

*The amount of hydrochloric acid used (20cm")

*The equipment used

*The time interval between each reading

I will also carry out the same experiment three times to make sure that my results are as accurate as they can be.

Conclusion

I predicted the following:

"I predict that the reaction will become more rapid as the concentration of the hydrochloric acid increases. I think this because, as earlier stated, when the acid is highly concentrated there is more change of a reaction occurring. Therefore, a reaction with 2.5 molar of hydrochloric acid will be a lot...