Temperature
An increase in temperature produces an increase in the rate of reaction. A rise of 10º C approximately doubles the rate of reaction (according to the Q10 theory). When a mixture is heated, the particles move faster. This has two results. As the particles are moving faster they will travel further distance in a given time and so will collide more. Also, because the particles are moving faster a larger proportion of the collisions will exceed the activation energy and so the rate of reaction increases.
From the graph below you can see that the highest temperature (90°C) will have the most particles that collide because there collision time is the longest. The lowest temperature (20°C) will most likely have the least particles to collide and react because the collision time is very short.
If the Q10 theory is applied to this experiment then the rate of reaction should double as the temperature increases by 10°C. The rate of reaction is worked out by the following formula:
Product formed
Rate of reaction = Time taken to form product.
Surface Area of Magnesium
By breaking up the magnesium into smaller pieces, the surface area is increased, giving a greater area of collisions to take place and so causing an increase in the rate of reaction. When the surface area is low or small, the rate of reaction is lower because there is less Magnesium for the Hydrochloric Acid to react with, there is ‘less reacting’ area.
Concentration of Hydrochloric Acid
The more concentrated the reactants, the greater the rate of reaction will be. This is because increasing the concentration of the hydrochloric acid increases the number of collisions between particles and, therefore, increases the rate of reaction. For this experiment I am using 1M hydrochloric acid. If you look at my diagram you can clearly see that with the higher acid concentration you use, the more particles the acid has.
2 Molar 4 Molar
Pressure
When one of the reactants are gases an increase in pressure can lead to an increased rate of reaction. The increase in pressure forces the particles closer together. This causes more collisions and increases the rate of reaction.
Catalyst
Catalysts usually speed up a reaction; they remain unchanged at the end of the reaction. A catalyst, which slows down a reaction, is called a negative catalyst. Catalysts speed up reactions by offering a ‘alternative’ pathway for the reaction, i.e. one that has much lower activation energy. More collisions will, therefore, have enough energy for this new pathway
Prediction
I predict that when using prediction as a variable the collision theory will be correctly applied to my results. I think this because I have good evidence (Boltzman distribution curve). I also believe that it makes sense that the higher the temperature, the more energy the particles will have to collide and react successfully.
I predict that the Q10 theory will be relative to my experiment a great deal and that it will work. The Q10 theory is that for every 10°C the temperature goes up the rate of reaction is doubled.
The rate of reaction will increase when temperature and surface area of Magnesium is increased and acid concentration of Hydrochloric Acid is lowered.
Method
1. Collect equipment: -
Magnesium,
1M Hydrochloric Acid,
Thermometer
Test tube,
Pipette,
Vernier Callipers,
Kettle,
Water,
Emery paper (This may affect the rate of reaction when surface area of Magnesium is applied is that Magnesium oxide (Magnesium Oxide) can affect the surface area of Magnesium. When oxygen reacts with the Magnesium, Magnesium oxide is formed which can ‘eat away’ slightly at the Magnesium. To prevent this I am going to ‘rub’ off any Magnesium Oxide with sand paper.)
Beaker and
Stop clock.
2.Boil water, when boiled pour in beaker. Measure 25cm3 of Hydrochloric acid with a pipette and put in a test tube. Put test tube in boiled water and wait until Hydrochloric acid has heated to 60°C (check with thermometer) Use emery paper to rub off any magnesium oxide.
3. Drop 1cm of Magnesium into the Hydrochloric acid. AS soon as Magnesium is dropped into Hydrochloric acid start stop clock. Place bung over the top of the test tube. The bung has tubing in it, which lead into an upside-down measuring cylinder.
4. After 20 seconds measure amount of hydrogen in the upside-down measuring cylinder. Record results then repeat the same experiment twice.
5. Do the experiment 3 times for each of these temperatures: 20°C, 30°C, 40°C, 50°C and 60°C.
Fair Testing
My experiment will be fair because I am only changing one variable (temperature). I am changing the variable five times (20°C, 30°C, 40°C, 50°C and 60°C) and will do each experiment three times, to make sure the results are accurate. I will be very exact with all my measuring; I am using vernier callipers to measure 1cm Magnesium and a pipette to measure 25cm3 Hydrochloric acid.
For each 1cm Magnesium I will rub off any Magnesium Oxide with emery paper so the Magnesium is a pure a possible.
Conclusion
From my experiment you can see that the collision theory has been applied correctly. I predicted that the higher the temperature, the higher the rate of reaction. This is because when the Hydrochloric Acid particles are heated more particles reach activation energy therefore more chance of the Hydrochloric Acid reacting successfully with the Magnesium particles to cause bonds.
If you refer to my results then you can see that as the temperature increases the rate of reaction does as well; at 20°C the rate of reaction is 0.135cm3-1 and at 60°C the rate has gone up to 0.545. To increase the rate of reaction you need to change one of four things, temperature, acid concentration. Catalyst and surface area. I chose to change the temperature as I thought it would have the most significant difference on the rate of reaction.
My qauntative theory. Q10 theory unfortunately was not applied correctly. If it would have worked my results would look like this: -
From this table you can see that the Q10 theory did not work with this experiment, at the start of the experiment (20°C) the Q10 theory is applied correctly this is only because there is no previous temperature to double. I don’t think this worked because I now realise that when temperature is increased the rate of reaction only alters a little bit and with the Q10 theory the rate of reaction alters quite a lot.
Evaluation
I believe that my general procedure was efficient; I did everything methodically and accurately. I measured the Hydrochloric Acid with a pipette and precisely measured the Magnesium with vernier callipers. I also followed my method closely, so I didn’t do anything to create any anomalous results. I don’t think any of my results were particularly odd, but if you see my graph the 30°C result looks slightly out of place on the line of best fit. Apart from this my results were mostly constant and steady. I repeated all my results three times because if a odd result did occur I could compare it to the two other results and maybe do it again. In some of my repeats there were a few slightly odd results, but nothing too major to make a difference.
If I were to do this experiment again I would more research in the form of preliminary work and I would use another variable as well as temperature, to see if temperature is what affects the rate of reaction the most I would also repeat the results at least six times to get a better average. If I were to do any further work on this experiment, I would do more research into how Hydrochloric Acid and Magnesium react with and without temperature changes, I would see if the Q10 theory could be proved with another experiment and compare the two experiments. I would also improve the amount of gas is collected to do this I would use
a video camera to allow you to work out the volume of gas more accurately every 20 seconds as you could use the freeze-frame facility.
