Temperature Change
When the temperature is raised these things may happen:
- The peak will be at a higher energy
- The peak is lower
- The peak is broader
- There is a large increase in the number of particles which higher energies
Catalysts
A catalyst is a substance that speeds up a reaction with out changing its chemical elements.
Background Knowledge / Preliminary Experiment
We carried out a preliminary experiment to get the idea of what we were going to do.
During my preliminary experiment in which sulphur was made the speed at which the precipitate of the solid was produced was used to measure the speed of the reaction.
Na2S2O3(aq) + 2HCl(aq) →2NaCl(aq) + H2O(i) + SO2(g) + S(s)
Prediction
I predict that as the temperature is increased the rate of reaction will increase. I also predict that as the concentration of the sodium thiosulphate increases the rate of reaction will increase. When the temperature is increased the particles will have more energy and this would enable them to move faster. This will make them collide more often and with more energy. Particles with more energy are more likely to overcome the activation energy barrier to reaction; this would make them react successfully. If solutions of reacting particles are made more concentrated there are more particles in the area.
Method
Experiment 1 - Changing the concentration
5 cm3 of HCl (at concentration 1 mol./dm3) and 15 cm3 of sodium thiosulphate (at varying concentrations – 10 to 35 g/dm3) are poured out into two measuring cylinders and then poured into a conical flask, which is placed on top of a board marked with letter X. The stopwatch will now be started. When the mixture has turned sufficiently cloudy so that the letter X can no longer be seen the stopwatch will be stopped and the time will be recorded. The experiment is repeated with all the concentrations. The whole procedure is then repeated. In order for my findings to be valid the experiment must be a fair one. I will use the same standard each time for judging when the X has disappeared. I will make sure that the measuring cylinders for the HCl and thiosulphate will not be mixed up. The amount of HCl will be 5 cm3 each time, and the amount of thiosulphate will be fixed at 15 cm3.
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Safety Measures
The following safety measures will be taken:
- Safety goggles will be worn.
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Be aware that HCl is HARMFUL.
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Be aware that SO2 is produced. We will wash the substances away after use.
- Extractor fan will be kept on at all times.
Collision Theory
The two requirements for a reaction to take place are activation energy to be reached and successful collisions to take place.
As the solution gets more concentrated the ions are closer together therefore they will collide more often and more successful collisions are likely, therefore as the concentration decreases fewer successful collisions take place and the rate of reaction slows.
Apparatus List
- Water Bath
- Hazcards
- Plastic Pipette
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Beaker (250cm3)
- Wash bottle
- Distilled water
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Measuring cylinder (100cm3 and 10cm3)
- Flask (250cm3)
- HCl (1 Molar)
- Stopwatch
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Na2S2O3
What I Will Do With My Results…
With the results I will use them for creating the following items:
- Plot some graphs (Perfect curve, line of best fit) On the axes, I will write: The rate (y axes) and Average time (x axes).
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I will also plot the following graph: average times (y axes) and concentration of a) Na2S2O3
b) HCl
Strange Results… Potential Variables…Anomalies
These are results that are completely out of the blue and therefore most likely to be wrong! I will keep a close eye out for these in my experiments and if I do spot any the experiment will be repeated.
