It can also provide a surface for the molecules to attract to, thereby increasing their chances of collision.
Catalyst is very important in industry because they speed up reaction even at low temperatures. This means that less fuel is need, so money is saved. The optimum temperature for a catalyst is at the degree of 37. If the temperature is too high the catalyst will denature.
Temperature
Increasing the temperature of a solution means they gain more kinetic energy; therefore the particles take in more energy causing them to move faster and collide more often. A small increase in temperature causes significant changes to the distribution of energies, so the rate of reaction is increased. However, at low temperatures, particles of reacting substances do not have much energy and the particles move fairly slowly. This means particles will collide less often with less energy and less collisions will be successful.
Rate of reaction
Concentration
If the concentration of an acid is increased, the reaction will increase. It is easy to see why:
Diagram 1 Diagram 2
Diagram one shows a soluition that includes water molecules, acid particles and magnesium atoms. In a dilute acid there are fewer acid particles. This means there is a less chance of an acid particle colliding a magnesium atom.
However, in diagram two is shows the acid is more concentrated as there are more acid particles in it. There is now more chance of a successful collision occurring, between the magnesium atoms and acid particles.
Concentration of Acid
In this experiment I am going to find out how the rate of reaction between sodium thiosulphate and hydrochloric acid is affected by changing the concentration.
The equation to this is as followed:
sodium + hydrochloric -----------> sodium + sulphur + sulphur + water thiosulphate acid chloride dioxide
Na2S2O3(aq) + 2HCl(aq) ----------> 2NaCl(aq) + S(s) + SO2(g) + H2O(l)
Prediction
I predict that as I add 1cm³ of hydrochloric acid and an increase amount of water each time to the solution of sodium thiosulphate, the time it takes for the reaction to occur, with increase, this means the rate of reaction will decrease.
This is because as the solution of hydrochloric acid becomes more dilute with water, the reaction will decrease, as the particles of hydrochloric acid will not collide with the particles of sodium thiosulphate as often.
Equipment
In this experiment, I will be using the following equipment safely and accurately.
- A small piece of paper (with cross)
- Measuring cylinders
- Beaker
- Conical Flask
- Pipette
- Stopwatch
- Pair of goggles
- Burettes
- Water (distilled)
- Hydrochloric acid
- Sodium thiosulphate
Method
1) Firstly, draw a black cross on a piece of white paper. Then place a beaker filled with 50cm³ of sodium thiosulphate on top of the piece of paper, making sure the cross is easily seen through the solution.
2) Add 1 cm³ of hydrochloric acid using a pipette, and start off by adding no water to the solution of sodium thiosulphate.
3) Start the stopwatch as soon as both the Hydrochloric acid and the sodium thiosuphate is added. At each interval, add 2 extra cm³ of water. Swivel the mixture and time how long it takes for the cross to be completely obscured. His mixture should turn cloudy, if not yellow.
4) Then empty out the contents of the conical flask, clean it out, and dry it. Repeat this three times, and find an average result.
Fair test
In this experiment we are trying to find the rate of reaction using concentration as a factor, so there is a number of things we need to make sure we do to keep it a fair test.
Firstly, we need to keep a chemical at a constant concentration. So, in this experiment we have chosen to keep Sodium thiosulphate and hydrochloric acid at a constant concentration.
Next we must make sure that the solution is kept at a constant volume throughout the experiment. If the volume is different, then it could give different results to if it was at a constant volume.
We must also make sure that we add both the water and the hydrochloric acid at exactly the same time (into the conical flask with the sodium thiosulphate in it), or it could affect the results of the experiment.
We must start the stop watch at the exact time as we put the water and the hydrochloric acid into the conical flask. To do this it is a lot easier if there are two people doing the experiment, so one person can put the two substances in the sodium thiosulphate, and one person can start the stop watch.
Another thing we must do is to make sure that the conical flask is completely clean and free of any water or any other substance before we attempt to start the next experiment.
Safety
There are a lot of safety issues we must follow by in this experiment also.
We must remember that the substances, which we use in this experiment, can be very harmful if used the wrong way.
When we do this experiment, it may be necessary to wear safety goggles, as things are very unpredictable, and even though it is very unlikely that the solution would come out of the conical flask during the experiment, one must still be cautious of spills.
We must make sure that coats and bags are all out of the way while doing the experiment. Ties and hair should be tucked out of the way, so they do not make contact with any of the chemicals. It would also be preferable to wear a scientific apron, however this is not essential.
We should also try our best not to spill any chemicals, and we must not eat or drink in the lab while dealing with these harmful chemicals, as they can get on to our hands.
Analysing Evidence
It is obvious to notice from the graph that as the concentration of the acid solution decreases in volume, the rate of reaction reduces. This is true because in a dilute acid there a re fewer acid particles. This means that there are less acid particles colliding with the sodium thiosulphate particles, therefore, there is a slower rate of reaction.
If the concentration of a solution is increased, there are more reactant particles per unit volume. This increases the probability of reactant particles colliding with each other. The rate of reaction depends on how often and how hard the reacting particles collide with each other.
Low concentration
There are fewer reactant particles, therefore the probability will collide is low.
High concentration
There are a lot more reactant particles; therefore the probability that they will collide is much greater.
The time it takes for the cross to disappear relies on the concentration of the Hydrochloric acid. As the experiment continued, the water to acid ratio was bigger. If there is more water to acid in a solution, it means that there is more water molecules in it.
The fact that there are more water molecules knocking about between the sodium thiosulphate means that collisions between the hydrochloric acid are more likely to occur.
My results coordinate very well with my predictions because I predicted that when I added 1cm³ of HCl acid and an increase amount of water into the flask with the Sodium Thiosulphate, I thought that the cross would disappear a lot slower. And by looking at my results on the graph I believe that my results do agree with my prediction. In conclusion to this experiment I find that my prediction was correct.
Evaluation
My results are accurate because when I read the collision theory it told me exactly what my results told me.
The results I obtained from the experiment were accurate; this indicates that the experiment I preceded was successful.
As I performed my experiment three times, the individual results were reasonably reliable excluding the first attempt that I did, as they were approximately I minute apart. This may result to an increase of the appropriate amount of sodium thiosulphate, hydrochloric acid and water added.
I would also make my experiment a fair test, by making the results more accurate. I would do this by using clean equipment, and using the right amount of acids.
From looking at the graph, I have noticed that there are two anomalies. The first was at the concentration of 16 g/cm, and the second anomaly was at the concentration of 32 g/cm. There are many reasons towards this, first of all, the experiment may have not been a fair test, simply because I may have not cleaned out the flask, or, the amount of acid may have varied according to what is was suppose to be.
If I were to do the experiment once again, I would take into consideration the amount of sodium thiosulphate used, by using more acid; the whole experiment will take less time to do.
