I also made it a point to wear a sort of mask covering I mouths as the fumes of HCl acid were very strong. I was also very careful not to run in the room in which the experiment took place as this could cause accidents.
Hypothesis
There are many factors which affect the rates of reaction. These are raising the temperature, catalysts, increasing the surface area of a solid, increasing the concentration, increasing the pressure, providing more light and decreasing particle size I will be concentrating on temperature. But why does temperature have such a large effect on the rates of reactions?
The answer to this is found in the collision theory. That is, for a reaction to occur, according to the collision theory, there are three things which must happen first. These three basic ideas of the collision theory are:-
- Molecules react by colliding
- There is a certain way in which the particles must collide (orientation)
- Collisions must occur with a certain amount of energy called activation energy
These three factors are important aspects of the collision theory. The first point, molecules react by colliding, is a basic concept in the theory. It is true that for any reaction to occur the molecules have to collide. The application of heat enables the molecules to move faster hence making the collisions more and more frequent. The fact that the molecules collide more, when heat is applied, allows the bonds to be broken, consequently causing a reaction. It is true that for new bonds to be made, old ones have to be broken, therefore when collisions are more frequent the barriers, which prevent a reaction, are broken.
Along with collisions the orientation of the collisions also plays an important part in causing a reaction. The molecules have to run into each other in a certain way and in a certain direction to aid a reaction.
Applying heat to a reaction provides the molecules with more kinetic energy this energy quickens the reaction. For a reaction to occur between two molecules they have to have a certain amount of minimum energy, this energy is known as activation energy. When a substance is heated the molecules in it vibrate more fiercely providing a lot of energy. This proves that raising the temperature definitely quickens the rate of a reaction. The Maxwell-Boltzmann distribution shown below illustrates the amount of energy a number of particles possess. The graph only applies to gases, but conclusions which I may draw from it are true also for reactions which involve liquids.
The area under the curve represents the number of particles present.
In the diagram below the activation energy is labelled. The graph labelled T is at the original temperature. The graph labelled T + t is at a higher temperature.
As is evident from these graphs, raising the temperature almost doubles the amount of particles possessing activation energy or more. This is shown by the area to the right of the activation energy line. The area under the graphs remains constant as the number of particles present is the same throughout.
Conclusively it can be said that increasing the temperature most definitely increases the rate of a reaction as there is a large increase in the number of high energy collisions. It is due to these collisions, which possess at least the minimum energy required for a reaction (activation energy), that I have a reaction. Increasing the temperature for approximately 10ْ C almost doubles the time taken for a reaction to happen.
The Results Obtained
After I had carried out the experiment these were the results I obtained. The first table shows the results I got for every try I took (three in all). The second table shows the average time taken for each temperature. I obtained this by finding the mean of the three results for each temperature
The bar graph below represents the results I got.
This graph denotes the fact that as the temperature gets higher the rate of the reaction decreases. The same results may also be shown on a line graph which is shown overleaf.
This graph shows a negative correlation. This shows that as the temperature increases the time taken for the reaction decreases.
Results Analysis
Through all my results it is evident that temperature has a large effect on the time it takes for a reaction to occur. My hypothesis was correct; raising the temperature meant raising the rate of the reaction, hence making the reaction faster.
Considering my results it seems that the difference between two consecutive results seems to get smaller and smaller, for e.g. 50.3 – 29.54 = 20.76 and 17.44 – 15.09 = 2.35. Therefore the dramatic difference is evident.
Looking at the former graphs I have drawn up a negative correlation is evident. The line graph would form a perfect curve if it wasn’t for the fourth results. Something must have gone wrong when I were experimenting the rates of reaction with the temperature at 40ْ C. The results for this temperature are out of place. This could have been due to an error when doing the experiment at this stage.
Overall my prediction was correct. It is true that for a reaction increasing the temperature quickens the time taken for the reaction to be completed. This fact may be put to use in industrial processes. For processes which require a reaction to happen quickly, increasing the temperature has a large effect, as doing so, like I explained in my hypothesis, increases the energy of a molecule and causes it to vibrate faster. Doing so increases the frequency of the collisions. As these collisions increase the molecules come into contact more often, hence causing the barrier, preventing the reaction, to be broken. Increasing the temperature also provides molecules with at least the activation energy required for the reaction.
Evaluation
Overall my method worked rather well. I feel this because my results are the ones I expected. My results are also clarified by scientific theories such as the collision theory. My method was put to use logically and in an orderly manner. Although when carrying out my experiment I did experience problems. When placing the sodium thiosulphate on the Bunsen burner it was quite a task taking the sodium thiosulphate on to the next table, placing it on the cross and then quickly adding the dilute hydrochloric acid. This may have caused I results to be a little biased as, during the process of bringing the sodium thiosulphate to the next table and then adding the dilute hydrochloric acid, the liquid may have cooled a bit.
To make the experiment better and my results more reliable I would have used a beaker with a less exposed surface area, this would have caused less heat loss. I would have also used a tile with a cross on it instead of using just a paper. This is due to the fact that using a paper I had to be extra careful not to spill anything on it because if I did so the cross would darken, hence making the results unreliable. As well as this I would have done the experiment on a less humid day as the room temperatures were pretty high.
Generally my evidence is pretty good. However there is an error with fourth result where I heated the sodium thiosulphate until it reached 40ْ C. This result may have been caused due to carelessness on my part. It could have been that I were too slow in getting the liquid away from the Bunsen burner, during the process some of the heat may have escaped through the beaker.
On the whole I feel that my evidence is sufficiently reliable. It closely supports my hypothesis and is backed up with scientific theory. However to ensure my results are more reliable I could have done the experiment more than three times to obtain more accurate results.
Conclusively I think I did pretty well especially considering the time and resources available to me. My results were backed by my hypothesis and seem to be reasonably reliable.
Bibliography
- Internet sheets on the collision theory – Enid Duckworth
- www. Courseworkbank.co.uk
