If the collision has enough energy the reaction takes place. Magnesium chloride and hydrogen are formed.
If the collision does not have enough energy, no reaction occurs. The acid particle bounces away again.
If there are lots of successful collisions in a given minute, then a lot of hydrogen is produced in that minute. So if the reaction goes quickly – it’s rate is high. If there are not many, its rate is low. The rate of reaction depends on how many successful collisions there are in an amount of time.
To change the rate of reaction the concentration of the acid should be increase and the reaction will happen faster.
In dilute acid, there are not so many acid particles. This means there is not much chance of an acid particle hitting a magnesium atom.
Here the acid is more concentrated- there are more acid particles in it. There is now more chance of a successful collision occurring.
The more successful collisions there are, the faster the reaction.
This idea also explains why the reaction between magnesium and hydrochloric acid slows down as time goes on:
At the start, there are plenty of magnesium atoms and acid particles. But they get used up during successful collisions.
After a time, there are fewer magnesium atoms, and the acid is less concentrated. So the reaction slows down.
This means that the slope of the reaction curve decreases with time, as shown above.
If the reaction involves a gas, then increasing the pressure of the gas is the same as increasing the concentration of the gas. So a reaction involving a gas will go quicker at higher pressures.
The rate of reaction is also dependant on the reaction temperature, the surface area and the presence of a catalyst.
Why rate increases with temperature:
At low temperatures particles of reacting substances are heated, the particles take in energy. This causes them to move faster and collide more often. The collisions have more energy, so more of them are successful. Therefore the rate of reaction increases.
Why rate increases with surface area:
The reaction between the magnesium and acid is much faster when the metal is powdered as much more atoms are exposed so there is a greater chance of successful collisions.
Why catalyst increases the rate
A catalyst can speed up some reactions. In the presence of a catalyst a collision needs less energy in order to be successful, so the reaction goes faster. Catalysts are very important in industry because they speed up reactions even at low temperatures. This means less fuel is used and money is saved.
Experimental Plan:
The reaction to be studied is:
2H O 2H O + O
As the reaction proceeds oxygen gas is produced. A simple way of following this reaction is to measure the volume of oxygen produced. The rate can be calculated using the equation:
Rate (cm³/sec) = Change in volume (cm³)
Time (seconds)
There are 5 things, which influence the rate of reaction:
Temperature
Concentration
Pressure
Surface area
Catalyst
In this experiment I have chosen to investigate the effect of changing the concentration – this is my chosen independent variable.
I will be measuring the change in volume of oxygen produced. The volume of oxygen will be my dependant variable.
The Temperature, Pressure and Surface area all affect the rate of reaction in my experiment. However I am not investigating these. To make sure they don’t influence my results I must make sure they stay the same throughout the experiment.
Therefore the temperature, pressure and surface area are my controlled variable.
The Temperature will be room temperature
Pressure will be room pressure
The same amount of MnO will be used in each experiment so the Surface Area will be the same
In each experiment 0.2g of MnO is used are 20%, 40%, 60%, 80% and 100%. In the experiment I am going to change the concentration of the hydrogen peroxide to see how it affects the formation of oxygen.
Readings will be taken over a period of 3 minutes. Each experiment will be repeated 3 times and an average result taken. This is to make sure that my results are accurate.
Justification:
The particles in the liquid move around continually. Here a hydrogen peroxide particle is about to collide with a manganese atom.
If the collision has enough energy, the reaction takes place manganese dioxide and hydrogen are formed.
If the collision does not have enough energy, no reaction occurs. The hydrogen peroxide particle bounces away.
Apparatus:
Safety glasses
Beaker
Basin
Conical Flask
Measuring Cylinder
Bung
Stop Clock
Concentrations of Hydrogen peroxide
Catalyst
Beehive
Method-
- Collect a basin full of water
- Collect conical flask and beehive
- Place bee hive in the water, with the tube from the conical flask in it
- Collect stop clock
- Collect beaker with correct measurement of Hydrogen Peroxide
- Collect catalyst
- Then collect measuring cylinder and place on bee hive
- Add hydrogen peroxide and catalyst in conical flask and put bung over it
Record results of amount of oxygen formed every 15 seconds for 3 minutes.
Conclusion:
The results show very clearly that the rate of decomposition for Hydrogen Peroxide does increase as the concentration of Hydrogen Peroxide. This proves that my perdition is correct. The results are summarised in the table below.
Concentration of Hydrogen Rate of reaction (cm³/sec)
Peroxide
20% 0.284
40% 0.350
60% 0.384
80% 0.722
100% 0.895
From our results the rate of reaction is 0.284 when the concentrations 20%. If we increase the concentration of the Hydrogen Peroxide the rate of reaction will increase.
As the concentration of hydrogen peroxide increased this meant that there were more Hydrogen Peroxide molecules and therefore there was a better chance of them colliding with the MnO and decomposing.
Safety:
Hydrogen Peroxide – Don’t let near skins, irritating
MnO - don’t let near skin
Wear safety goggles
Tie long hair back
Sources of error
Possible sources of error include human error when measurements of the Hydrogen Peroxide or measuring out the MnO , there were no major errors.
Improvement:
To improve upon my experiment I could use a more accurate balance for weighing the MnO and take more care when measuring the Hydrogen Peroxide out.
Instead of repeating the experiment 3 times I could repeat it 5 times.
