As I mentioned before, the rates of reaction depends on four things. All four methods of increasing the rate of reaction can be explained in terms of increasing the number of collisions.
Temperature increases the number of collisions. When the temperature is increased, the particles all move quicker. If they’re moving quicker, they’re going to have more collisions.
Reactions only happen if the particles collide with enough energy. At a higher temperature there will be more particles colliding with enough energy to make the reaction happen. This initial energy is known as the activation energy, and it’s needed to break the initial bonds.
All reactions are exothermic in one direction and endothermic in the other. If the temperature is raised, the endothermic reaction will increase to use up the extra heat. If the temperature is reduced, the exothermic reaction will increase to give out more heat.
The affect of temperature on rates of reaction is important. Raising the temperature makes the rate of reaction faster. Because the temperature increases, the pressure of the molecules increase, causing them to move more faster which will then lead them to bump into each other more frequently. Therefore the molecules are reacting.
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.
Prediction:
I predict using my research and own scientific knowledge that as the concentration (mol) increases the faster the rate of reaction. This is because increasing the concentration means there are more particles present and this increases the chance of collision between the particles and therefore there would be a higher reaction rate.
This is a diagram of what I think will happen.
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,
Stopwatch,
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 five different concentrations that I will be experimenting with. These are: 0.1M 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 the average. I had to do the whole experiment three times to get a fair set of results.
The graph below is an overall graph to show the fair set of results to portray the results.
I have also created a Graph with the line of best fit to indicate the full results.
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 sulphate molecules are more likely to occur.
Sodium Sulphate particles
Low Concentration High Concentration
(Low Pressure) (High Pressure)
As you can see from the diagram above, 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 that 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 saw 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.