Catalysts
A catalyst will only work for a certain reaction, or groups of reactions. For the experiment I will be doing, there is no available catalyst. A catalyst slows down or speeds up the rate of a reaction by increasing or lowering the activation temperature that reaction works at. A catalyst is never used up in the reaction; this means it can be used over and over again. A catalyst can, however, become denatured. This happens in biological catalysts when the temperature goes above 50 Degrees Celsius. A biological catalyst is known as an enzyme. Manufacturers use catalysts to make a bigger profit on their products and it also helps in keeping the amount of fuels used down. A catalyst is usually a transition metal or a transition metal oxide.
Surface area
The more surface area a reactant has, then the faster the rate of reaction will occur. This is because the two types of molecule can only bump into each other were the liquid meets the solid face. So the larger the surface area of the solid, the faster the reaction will be. Smaller particles have a larger surface area than large particles even with the same mass of a solid. This is why smaller chunks of potato, for example, would cook faster than large chunks.
Pressure
This mainly applies to gases. Particles in gases are very far apart. For a reaction to happen, collisions between the particles need to be made. By decreasing the amount of space a number of particles have to move around in (increasing pressure) you increase the number of collisions between the particles. Once a reaction has started it will gather up speed very quickly as heat is produced.
Concentration
1/time
Concentration of sodium thiosulphate solution
The concentration of a substance is measured in molarity. This is how many atoms of that element there is in one litre of water. The higher the molarity of the acid then the faster a reaction will take place because the ions are closer together. According to my Chemistry textbook, if the molarity of the acid is doubled then the speed also doubles. The two are proportional.
Temperature
Temperature and the rate of a reaction are inversely proportional. This means that the faster a reaction takes place the shorter time it will take to finish.
Speed of a reaction ∞ 1/time
When we warm the sodium thiosulphate solution, the heat makes the sulphur form faster. There is a step increase in the speed of the reaction as the temperature is increased.
This graph shows that as the temperature doubles the rate of the reaction also doubles. Whilst the temperature is doubled the time for the reaction to happen is halved. This is because at a higher temperature the ions have more kinetic energy. Moving through the solution more rapidly, they collide with one another more often so there is a greater chance they will react.
Apparatus
- Tripod
- Thermometer
- Heatproof mat
- Bunsen burner
- Goggles
- Sodium Thiosulphate
- Beaker
- Paper
- Pen (to mark a cross)
- Sulphuric acid.
Method
- Set up apparatus
- Measure out 25ml sodium thiosulphate
- Heat up to desired temperature
- Add 5ml Sulphuric acid
- Record the results.
In this experiment I am going to go up in intervals of 5 degrees. This means taking the temperature at 20, 25, 30, 35, 40, 45 and 50 degrees Celsius. This amount of readings will ensure we get a detailed graph making it easier to spot the anomalous results and find patterns.
Fair test
To make sure I get accurate and real results I have to ensure I do a fair test. To do a fair test I must keep everything constant excluding the factor I am investigation (i.e heat). This includes:
- Concentration
- Amounts of solute and solvent
- Same stop watch
- Same cross on the paper
The only thing I will change very carefully is the temperature levels.
Results
Temperature ( oc) Time (seconds)
30 36
40 17
50 11
60 7
70 4.7
80 3.03
