What Affects the Rate of Reaction?

What affects the Rate of Reaction?

The reaction I will use for this test is:

2HCl(aq) + CaCO3(s) CaCl2(aq) + CO2(g) + H2O(l)

The possible variables for this experiment are the concentration of acid; the surface area of the solid reactant, the calcium carbonate by using chips or powder; and the temperature. Following are quick summaries on how changing each variable will affect the rate of the reaction.

By increasing the surface area you are increasing the amount of collisions that will take place in a section of time therefore increasing the rate of reaction. The use of powder calcium carbonate will give a larger surface area so that the rate of reaction will increase because the collision, where two different molecules bump into each other, has to happen at the liquid solid interface if the liquid solid interface is larger then more collisions will take place in a period of time making the reaction faster. If chips of calcium carbonate are used the opposite would happen, there would be a smaller liquid solid interface and therefore a smaller amount of collisions will take place in the same period of time.

By increasing the temperature you are adding more energy to the molecules. When the molecules have more energy they will be moving a lot more giving the opportunity for more collisions to take place, and more molecule will have sufficient energy for the reaction to take place, making the rate of reaction faster.

The possible measurements to take to find the rate of reaction are how much gas is given off and the before and after weight.

My Prediction -

The variable I have chosen is the concentration of acid.

I predict that by increasing the concentration of the acid you are increasing the number of acid molecules in a small area of space, this means that more collisions will take place and the rate of the reaction will increase, also the energy the molecules have will increase as the pressure is increased this means that the molecules that will be able to reach activation energy and more collisions will be successful. In reverse by lowering the concentration you are decreasing the amount of acid molecules in a small area of space, this means that less collisions will take place and the rate of the reaction will decrease, also by reducing the pressure you are also reducing the amount of molecules that will reach the activation energy required to make the reaction occur, making less collisions successful decreasing the rate of the reaction.

This theory is based on the collision theory.

Method -

1. The variable I am going to use is the concentration of acid. To measure the rate of reaction I am going to time how long it takes to fill a test tube with the gas product carbon dioxide.

2. Firstly I am going to place the calcium carbonate in a 400ml flask, before I carefully add the acid I will fill a container about the size of an ice cream tub (filled with approx. 700ml).

3. Then I will add the acid with the correct concentration, the measurements of the calcium carbonate and the hydrochloric acid are both going to be decided after the preliminary experiments to give increased accuracy in the experiment.

4. Quickly after the acid is put into the flask I will put a bung tightly in the neck of the flask with the delivery tube in it so no gas is lost because this will affect the timings and make the experiments unfair, also no gas should be lost into the container before the cylinder is full as this will have the same effect; with the end of the delivery tube in the water in the container with the 25cmÑ- measuring cylinder filled with water over the end of the delivery tube.

5. As soon as the first bubble enters the cylinder I will start timing, and when the cylinder is full and the first bubble goes into the water surrounding the cylinder I will stop timing. As we are using 2M of acid we will be able to dilute it to get a lower concentration of acid but not get a higher concentration than 2M.

To make the test safe I will:

* wear safety glasses and tie my hair back before experiment

* wear safety glasses for all of experiment until all equipment is packed away

* also be careful while handling the acid as it can cause small injury on skin

* be careful when handling glass as could break and cause injury

* if there is broken glass I will inform an adult and take further instruction

To make it a fair test I will:

* keep the amount of calcium carbonate the same in each trial

* keep the amount of hydrochloric acid the same only changing the concentration

* do three trials per each concentration to get fair results

* make an average rate for each concentration to make it easier to compare the rate of reaction for each concentration

* make sure I start timing and stop timing at the specific points mentioned earlier

* repeat every test that has odd results to make sure my results are fair and give the correct relation between the concentration of acid and the rate of the reaction.

Equipment -

* 400ml flask

* bung with attached delivery tube

* 25cmÑ- measuring cylinder

* large water tight container (needs to be able to hold at the 1litre of water)

* sensitive scales which measure to at least one decimal place

* calcium carbonate chips

* hydrochloric acid (2M)

The flask needs to be fairly small so the gas goes through the delivery tube rather than staying in the flask. I find it easier to measure more accurately with a smaller measuring cylinder as they tend to have more detailed measuring markings. The scales