At the higher temperature there are more particles with more energy than the activation energy, therefore there are more successful collisions per second and the reaction is greater.
- Concentration, particle size and pressure in gases
Increasing the concentration of a solution increases the rate of reaction. This is because, the higher the concentration, the more particles there are per unit volume. Therefore there are more collisions, hence more successful collisions per second and rate increases. Increasing the pressure of gases has exactly the same effect as increasing concentration and works the same way.
LOWER CONCENTRATION HIGHER CONCENTRATION
(Or Gas pressure) (Or gas pressure)
FEWER PARTICLES PER UNIT MORE PARTICLES PER UNIT
VOLUME.LESS SUCESSFUL VOLUME.MORE SUCESSFUL
COLLISIONS PER SECOND COLLISIONS PER SECOND.
LOWER RATE. HIGHER RATE
For reactions involving solids decreasing the particle size increases the surface area of the reactant. This means there are more solid particles exposed to the reaction at any one time. Therefore there are more successful collisions per second and rate of reaction increases.
GREATER PARTICLE SIZE SMALLER PARTICLE SIZE
SMALLER SURFACE AREA GREATER SURFACE AREA
LESS SUCESSFUL COLLISIONS MORE SUCCESSFUL COLLISIONS PER SECOND, LOWERS RATE. PER SECOND, HIGHER RATE.
These three factors can also be explained using an energy level diagram like the one used for temperature.
At the higher concentration in Curve 1 etc. there are more particles with more energy than the activation energy, therefore there are more successful collisions per second, and the rate of reaction is greater.
- Use of Catalysts
Catalysts are substances which increase the rate of reaction without being used up during the reaction i.e. the catalyst remains in the same form and amount at the end of the reaction as it was at the start. Catalysts work by causing a reaction to proceed by a different pathway. This pathway has lower activation energy than one without the catalyst i.e.
When the catalyst is present there are many more particles with more energy than the activation energy, therefore there are more successful collisions per second and the rate of reaction is greater.
FOLLOWING THE RATE OF A CHEMICAL REACTION
The rate of a chemical reaction can be followed by measuring the amount of a reactant used up per unit of time, or the amount of product produced per unit of time
E.g.
The rate of reaction between magnesium metal and hydrochloric acid
The equation for the reaction is
Magnesium + hydrochloric acid = magnesium chloride + hydrogen
Mg + 2HCl = MgCl2 + H2
In this reaction, Hydrogen is the easiest substance to measure because it is the only gas the hydrogen can be collected in a gas syringe or an inverted measuring cylinder full of water.
The volume of gas collected can be measured and recorded at regular intervals. Here are some typical results.
These results can be plotted on a graph:
The Disappearing ‘x’ Experiment
The Plan
For my procedure for the disappearing ‘x’ experiment I will be discovering the time taken for a x written on a piece of paper to disappear underneath a beaker filled with 5cm3 of hydrochloric acid and a changing amount of sodium thiosulphate and water. We will be investigating the rime taken for the ‘x’ to disappear based on the concentration of the solution. What we will be trying to discover is the affect the concentration of sodium thiosulphate will effect the time elapsed for the ‘x’ to disappear. I will perform the experiment three times and average the results to make it an even test.
The Apparatus#
The apparatus I needed to perform this experiment are listed below:
- Piece of paper with a cross marked on it
- A 250ml beaker
- A 50cm3 measuring cylinder
- Water
- Sodium thiosulphate
- Hydrochloric acid
- Stop clock
- Conical flask
Step by Step Method
- Fill a conical flask with 50ml of sodium thiosulphate
- Put the cross marked paper under the flask
- Add 5ml of hydrochloric acid to act as the reactant with the sodium thiosulphate
- As the last drop of acid enters the flask start the stop clock
- Stop the clock when the cross has totally disappeared
- Repeat this twice
- Fill the flask with 40ml of sodium thiosulphte and 10ml of water
- Add the hydrochloric acid
- Start the stop clock and record your results again
- Repeat this twice
And this is done with the sodium thiosulphate level dropping and the water level rising.
My Prediction
My prediction is that when the concentration of the sodium thiosulphate is more dilute the time taken for the cross to disappear because there will be less successful collisions per second thus resulting in more time being elapsed.
The Results
The results I have from the experiment are as follows:
The Graphs
Experiment 1
Experiment 2
Experiment 3
Overall average of data
Statistics about the experiment
Conclusion
I have concluded that the higher the concentration of sodium thiosulphate the faster the cross will disappear this is because the more of sodium thiosulphate there is the more successful number of collisions per second between the two reactants: hydrochloric acid and the sodium thiosulphate is depending on the amount of sodium thiosulphate in the solution, thus giving us the rate of reaction.