Concentration increases the number of collisions. If the solution is made more concentrated it means there are more particles of reactant knocking about between the water molecules, which makes collisions between the important particles more likely. In a gas, increasing the pressure means the molecules are more squashed up together so there are going to be more collisions.
If one of the reactants is a solid then breaking it up into smaller pieces will increase its surface area. This means the particles around in the solution will have more area to work on so there'll be more useful collisions. A catalyst works by giving the reacting particles a surface to stick to where they can bump into each other. This obviously increases the number of collisions too. Catalysts lower the activation energy of reactions, making it easier for them to happen. This means a lower temperature can be used.
An enzyme is a biological catalyst, which increases the rate of reaction. Enzymes are naturally occurring catalysts responsible for many essential biochemical reactions. Caseous and liquid catalysts are commonly dispersed in other substances known as catalyst support.
A catalytic action is a chemical reaction between the catalyst and a reactant, forming chemical intermediates that are able to react more freely with each other or with another reactant. Thiosulphate.
Prediction:
What I predict to happen in my experiment is that when I add 2M of Hydrochloric acid into the flask with the sodium Thiosulphate, I hypothesise that the cross will disappear a lot faster than when I add 0.5M of Hydrochloric acid.
This is a diagram of what I think will happen.
Concentration
Of HCl
Time In Seconds
I have predicted this due to the knowledge I have gained through my research. I found out that if I want to predict he rates of reaction, the collision theory would be useful to know about. This is because the collision theory is used to predict the rates of chemical reactions. The collision theory is based on the assumption that for a reaction to occur, it is necessary for the reacting species to come together or collide with one and other. Not all collisions however bring out chemical change. A collision will be effective in producing chemical change only if the species brought together own a minimum value of internal energy, equal to the activation energy of the reaction.
Furthermore, the colliding species must be positional so that they will suit the atoms and electrons. Therefore, according to the collision theory, the rate at which a chemical reaction proceeds is equal to the frequency of effective collisions. Because atomic or molecular frequencies of collisions can be calculated with some degree of accuracy only for gases (by application of the kinetic theory), the application of the collision theory is limited to gas- phase reactions.
The kinetic theory is the simplest model which is based on the assumptions that
1. The gas is composed of a large number of identical molecules moving in random directions, separated by distances that are large compared with their size.
2. The molecules undergo perfectly elastic collisions with each other and with the walls of the container (without any energy loss, but otherwise do not interact; and
3. The transfer of kinetic theory between molecules is heat. These simplifying assumptions bring the characteristics of gases within the range of mathematical treatment.
To do my experiment I need the following equipment:
Flask,
Measuring cylinder,
Beaker 1,
Beaker 2,
Stop watch,
Paper with cross marked on it and
Goggles.
Here is an illustration of my equipment:
I will need to take safety precautions such as using goggles at all times whilst doing the experiment. I will also have to do my experiment where it is fairly spacious and also I must wash my hands properly after having dealt with the chemicals.
I will be measuring the concentration of the Hydrochloric acid in molars (M). There are four different concentrations which I will be experimenting with. These are: 0.5M, 1M, 1.5M, and 2M.
These were my results after I carried out the experiment.
As you can see in the table, I have repeated these measurements and then taken an average. I had to do the whole experiment again to get a fair set of results.
On the next page there is a graph of the results I got.
What I found out in my experiment was that each time the concentration of the Hydrochloric acid increases the cross took less time to disappear. So when I added 2M of HCl acid the cross disappeared a lot faster than when I added 0.5M of the HCl acid.
Analysis of results:
By looking at my graph I can see that when the concentration of the Hydrochloric acid is increased, the time taken for the cross to disappear decreases. This means that the concentration is inversely proportional to the time taken for the cross to disappear.
The time taken for the cross to disappear relies on the concentration of the Hydrochloric acid. This means that the acid to water ratio is bigger. If there is more acid to water in the solution then this means that there are more hydrochloric molecules in it.
The fact that there are more HCl molecules knocking about between the water molecules means that collisions between the Sodium Thiosulphate molecules are more likely to occur.
Low Concentration High Concentration
(Low Pressure) (High Pressure)
As you can see from the diagram on the previous page, the more collisions that occur will increase the rate of reaction. The rate of reaction depends on how often and how hard the reacting particles collide with each other.
To sum all this information up basically the particles have to collide in order to react, and they have to collide hard enough as well.
My results coordinate very well with my predictions because I predicted that when I added 2 M of HCl acid into the flask with the Sodium Thiosulphate, I thought that the cross will disappear a lot faster than when I added the 0.5M of HCl acid. And by looking at my results on the graph I believe that my results do agree with my prediction.
Evaluation:
I believe that I do have an accurate set of results and that I do have enough results to be sure about my conclusion. My results are accurate because when I read the collision theory it told me exactly what my results told me.
I do not have any anomalous results which do not fit in the pattern because my predictions coordinated with my results very well.
My method of carrying out my experiment was fairly accurate. I made sure that I washed the beakers clean for the other two concentrations and the second experiment, I measured the same amount of solution in each time and I stopped the stopwatch as soon as I thought the cross had disappeared. I think that I should have used four different beakers for the four different concentrations because this would be fairer and there wouldn't be any water at the bottom of the beaker.
If I was to do the experiment again I could improve the accuracy and reliability of my results by having a range of different concentrations. Also I could use the same amount of beakers for the number of different concentrations I use.
If I had more time I could do extra experiments to investigate another factor such as the affects of temperature on a rate of reaction. Also I could investigate the affects of pressure on a rate of reaction
