So in order to break the energy barrier, there has to be enough activation energy so the reaction will take place. Temperature helps to do this as increasing the temperature of the system increases the range of kinetic energies, increases the average kinetic energy and increases the population of particles with more than the activation energy.
The two theories that affect temperature and the rate of reaction are the kinetic theory and the collision theory. The kinetic theory clearly states that the positioning and movement of particles in a substance increases if the temperature increases. Therefore, increasing the temperature increases the energy between the particles and makes them move around a lot more and collide more often with each particle colliding with enough energy to get it past the energy barrier. If this is done successfully, then the collisions should have no problem passing the requirement stated in the collision theory that are: To react particles must collide with enough energy to break existing bonds and with the correct orientation to bring reactive sites close together.
Bringing the reactive sites closer together means that the likelihood of a reaction occurring is increased so in a final research conclusion, increasing the temperature increases the rate of reaction speed.
In this investigation dilute hydrochloric acid (colourless) is added to sodium thiosulphate which gradually becomes cloudy as a result of the sulphur precipitating.
Prediction:
As I explained earlier, the rate of a chemical reaction is the speed at which it takes place. Temperature is a major factor in this as increasing or decreasing the temperature changes the movement of particles in a substance therefore changing the rate of reaction. When a reaction mixture is heated up, each particle in it acquires more energy and collides more with other particles. From my own knowledge and research, I can make the prediction that if you increase the temperature of a particular reaction, you increase the speed at which it takes place. This is simply because the particles carry more energy and collide more often where these collisions contain enough energy to break the energy barrier:
Temperature Raised
Particles, when moving faster, collide with greater power.
The reaction therefore becomes faster
Collisions between particles are useless unless they break the energy barrier and this is exactly what increasing the temperature will allow them to do.
To test how much the rate of the products will increase as the temperature increases the experiment will need to be carried out a number of times using different temperatures and recording the time taken for the sodium thiosulphate and hydrochloric acid to react at each of the different temperatures.
Apparatus:
The equipment I need to carry out the work and to obtain my results is:
· Sodium thiosulphate solution
· Hydrochloric acid
· 250cm conical flask
· -5 C -110 C thermometer
· 10cm /50cm measuring cylinder
· Heat proof mat
· Bunsen burner
· Tripod
· Stop clock
· The black cross
· A pair of Tongs
Safety Precautions:
Throughout this experiment, I made sure that safety was one of my top priorities. I wore goggles at all times to protect my eyes; I had to pour the reactants out extremely carefully as hydrochloric acid is an irritant where as sodium thiosulphate poses no threat to me.
Method:
- Put safety goggles on.
- Get all the equipment ready
- Pour out hydrochloric acid and sodium thiosulphate in separate beakers
- check the stop clock is functioning well
- Assign each member of the group with a job
- Pick 5 temperatures to use in the experiment
- Label the two beakers one “hydrochloric acid” and the second “sodium thiosulphate”
- Place a Bunsen burner under a flask containing water. This is known as a water bath
- Heat until desired temperature is reached
- Once temperature is reached pour the both reactants into the conical flask.
- Start the stop watch once pouring the last reactant
- Measure the temperature of the start, middle, and end of the reaction
- Record the results
- Repeat this for each temperature 3 times.
Observation:
All rate of reaction experiment have visible results and this experiment is no exception. When I added the hydrochloric acid to the flask I observed immediately at each temperature to see the changes or reactions that were taking place between the particles.
When observing the experiment, the changes I saw take place were the tone of the sodium thiosulphate/hydrochloric acid solution. At the initial temperatures, which were quite low, the solution became very foggy and misty but only after a fairly long time the cross was not visible. At the higher temperatures, the solution became fogy very quickly and in both cases, the solution continued to get foggy until the black cross was not visible. I could not see through the solution at all. The colour of the solution went from a clear colourless liquid to a yellowish-green colour and at the higher temperatures, the colour changed almost immediately. I did not see any gas given off or any vigorousness in the actual reaction. The change in colour was smooth and there was no sound made when it happened.
Fair Test:
To make my experiment a fair one, I had to look at a lot of things. Firstly, I looked at the factors that may have affected how well the investigation would work and these were things like using different equipment or doing the actual experiment in different conditions i.e. a colder/hotter environment. To combat this, I made sure that upon repeating the experiment, I used the exact same equipment and done it in the exact same environment to make absolutely sure that the experiment was fair at each temperature.
I think that these were both very important factors because they could affect the results severely and leave me with an anomalous when I should only have correlating results. To ensure fair and accurate results, all of the factors that can affect my results need to be controlled.
Reliable Results:
To make my results reliable, I am going to be doing each temperature 3 times between the ranges of Room Temperature to 70 C. That’s five different results altogether for the temperatures and the average that I will make from the three primary results that I record.
I will also make sure that each temperature is calculated to as accurate it can be as recording a result past the required temperature can mean unreliable results which make the entire investigation void as one result is not calculated correctly
Results:
I have decided to record my results in a table with a graph that is on a separate piece of graph paper.
Analysis of Results:
From my results, I notice that there is a considerable difference in the time for the cross to disappear from the lower temperatures to the higher temperatures. All of the times are pretty much the same for the three different recording indicating that the experiment was a pretty successful one. There is anomalousness result; I think this might have been cause as my group and I Complete the experiment in two different day. This may have changed the atmosphere of the room.
The reaction between Hydrochloric acid and Sodium Thiosulphate
When dilute hydrochloric acid is added to sodium thiosulphate solution, a fine deposit of sulphur is formed. The sulphur makes the solution cloudy. As more and more sulphur is formed, the solution becomes more and more cloudy. Soon it becomes impossible to see through the solution. The balanced equation for this reaction can be seen below.
Sodium + Hydrochloric Sodium + Water + Sulphur + Sulphur
Thiosulphate Acid Chloride Dioxide.
Na2 S2 O3 (aq) + 2HCL (aq) 2NaCL (aq) + H2O (l) + SO2 (g) + S(s)
Conclusion
From my results, I have come to the conclusion that if the temperature of a solution is raised, so is the time for the reaction to occur. The cross disappeared more rapidly as the temperature rose and I think this was due to the increase of energy between the particles and an increase in energy between collisions that successfully passed the energy barrier. This released the sulphur quicker and in larger doses, which turned the solution cloudy thus making the cross invisible.
At the lower temperatures, the time for the cross to disappear was less because the particles did not have as much energy as they did at the higher temperatures. At these temperatures the particles are colliding with much more energy and thus the reaction that releases sulphur works and now releases more sulphur at a much quicker rate thus increasing the rate at which the cross disappears.
Heat from Room Temp. HEAT:
Linking Prediction to Conclusion.
My original prediction was that if you increase the temperature of a reaction, you decrease the time it takes to occur. And, from looking back on my results, I can see that this hypothesis was correct as the time for the cross to disappear decreased as the temperature rose. My conclusion matches my prediction very well overall, and my results clearly show this where at 30, the time for the cross to disappear was 1min29sec seconds and at 70 C the time for the cross to disappear was 15- a difference of about 1min04seconds. The particles were moving around with more energy; enough to break the energy barrier and for a reaction to occur as the temperature rose.
Evaluation:
I think that this experiment has gone very well for me. My results were of a particularly accurate standard as I did each temperature the reaction was taking place three times and calculated an average from these times. There was only one strange result (anomalies) within my results table and I think this was caused by the change in atmosphere.
I think that I could have repeated my results more however for the reason that I feel although the experiment was repeated three times, the most accurate results in experiment can only come from constant repeatability which I did not display in my experiment. That said, the time allocated did not allow me to do so and I believe as an improvement of what I could do if I did the experiment again, I would have to say that, with more time, I would repeat the results further for even more accurate and reliable results.
I believe that I could have improved the method by making it more specific. I stated clearly all the various methods I took in setting the experiment up but I could have been more specific to how all the apparatus was used and perhaps why I used the apparatus I did as well.
I believe that I did get a suitable range of results for this experiment. I recorded results from temperatures that ranged from Room Temperature to 80 C and I think that this is a very good range to see how temperature affects the rate of reaction. However, I feel that this also reduces the chance of knowing if anything changes if the temperature reaches a certain point. Perhaps doing the temperature even higher would enhance my results but this is also quite dangerous so I cannot really say that I could have improved the range of my results.
Some other areas in the experiment that I feel I could have improved on were factors like controlling the stopwatch and measuring the amount of sodium thiosulphate and hydrochloric acid. There is lots of room for human error here. However the inaccuracies due to them were negligible because I paid close attention to these during the experiment.
Overall, this investigation has been a very successful one. I feel my results and analysis have been as accurate and reliable as they could have been under the time allocated. However I feel with extra time, I could have repeated the experiment and made it even more accurate and adapted it to try other variables i.e. concentration or adding a catalyst. These are the ways that I could expand on the original question.
Extending the investigation:
If I were to extend this investigation I would repeat the same type of experiment but change reactants to see how the temperature affects the rate of the reaction.
I would like to investigate the effect of temperature on the break down of hydrogen peroxide using celery tissue to supply the enzyme, catalyst. This would show greater depth into the topic and hopefully provide more conclusive results as to the conditions needed for the optimum yield of the increase in temperature would also decrease the rate of reaction.
From background research it is possible to discover that a rise in temperature increases the rate of enzyme-controlled reactions; a fall in temperature slows them down. In many cases a rise of 10oC will double the rate of reaction, but above 50oC the enzymes, being proteins, are denatured and stop working.
Knowing this it is possible to compose an experiment which will test if the above information is true for the enzyme, catalyst and work out the temperature at which the rate of reaction is highest.
Prediction
It is predict that the enzyme catalyst will only work at temperatures above 10oC and below 50oC. The optimum reaction rate will lie somewhere between 30oC and 40oC. As catalyst is an enzyme, which is used in the body, it is likely to have a high yield at 37oC, which is body temperature.
The predicted graph shows how the rate of reaction doubles as the temperature increases by 10oC and how below 10oC and above50oC the catalyst is denatured and does not function.
Method
The apparatus would be set up in the same way as the experiment for substrate concentration only using an ice bath or Bunsen burner to get the catalyst solution to the required temperature.
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Use 10cm3 of the catalyst solution and place in a chronicle flask.
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Cool to 10oC using an ice bath.
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Put 10cm3 of hydrogen solution into the chronicle flask.
- Leave to react for 1 minute.
- Record the results.
Repeat for 20, 30, 40, 50 and 60oC. Work out average O2 produced for each temperature and rate of reaction. Draw graphs using the results collected. From the graphs conclusions can be drawn as to the nature of catalyst and the best conditions needed for the fastest reaction rate.
