Chemistry Coursework Robbie Lloyd
Planning
Introduction:-
The enthalpy change of combustion of a fuel is a measure of the energy transferred when one mole of the fuel burns completely. A value for the enthalpy change can be obtained by using the burning fuel to heat water and using fact that 4.2J of energy are required to raise the temperature of 1g of water by 1ºC.
The aim of this experiment is to find the enthalpy change of combustion of a number of alcohols so that you can investigate how and why the enthalpy change is affected by the molecular structure of the alcohol.
The apparatus to be used:-
- Small copper can or other metal container to act as a calorimeter.
- Thermometer that measures to 0.1ºC.
- 100cm3 measuring cylinder.
- Spirit burners containing:-
- Methanol
- Ethanol
- Propan-1-ol
- Butan-1-ol
- Balance
- Bunsen burner
- Wooden splint
- Draught shielding
- Clamp and stand
- Water
- Heat proof mat
Equation for the combustion of alcohols:-
Alcohol + Oxygen Water + Carbon dioxide
E.g. Combustion of methanol
CH3OH + O2 CO2 + 2H2O
The method to be use for the experiment:-
- To begin with prepare a table remove all items of stationary from the surface and place them in bags, leaving only the paper and pen that are to be used to record the results. Remove bags from under the desks and place them in the designated positions.
- With the exception of the scales collect all the apparatus above, and place them on the prepared table.
- Switch the scales on, wait until the balance has settled, once the balance has settled press the tare button to ensure that the balance reads 0.00 and the balance registers the entire weight of the spirit burner alcohol. Weigh the alcohol in the burner to two decimal places with burner lid on. This weight should be recorded straight away in the table below, to ensure that a simple mistake in the recall of a figure weight doesn’t corrupt the reliability of the final findings.
- The weighed alcohol should be placed with the equipment on the prepared desk.
- Next 100cm3 should be carefully measured out with the use of the measuring cylinder.
- This water should then be carefully poured into the calorimeter, (no water should be present before hand and if the calorimeter has been previously used it should be dried with a cloth as it could affect the results). The lid should be placed on to prevent any water being lost through evaporation before and after the heating.
- The equipment should then be set up as seen in diagram 1. However before the draught shield is put in place calorimeter should be positioned exactly 10cm above the flame.
- This is to ensure that the same distance is present between each of the alcohols and the water that it is heating. Keeping this constant between different fuels ensures that the same amount of energy will be lost to the surroundings for each fuel.
- (Because the specific heat capacity is a single value, if the volume of air in between the flame and the calorimeter is kept the same, then the same amount of energy is needed to heat the surrounding air. Hence since this energy loss is constant for all the fuels it can be disregarded to a certain extent)
