Heat of Combustion

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Chemistry – Heats of combustion.

To determine the heats of combustion of selected alkanols and to use this information to determine the heat of combustion for a longer chain alkanols.

Formula
ΔH=-mCΔT Heat of combustion
ΔH/n = molar heat of combustion.

Materials
-100 degrees thermometer
-glass stirring rod
-aluminium beaker
-electronic balance
-bosshead and clamp
-retort stand

Method
1) Set up the apparatus as shown above.
2) Measure the weight of aluminium can
3) Use the electronic balance to calculate the mass of water as 100 g 4) Pour the water in the aluminium can
5) Record the initial temperature of water, initial mass of the spirit burner using an electronic balance. 6) Adjust the height of the clamp so that the tip of the flame touches the aluminium can. 6) Light the alkanol for 3min.

7) Record the final mass of the burner, and final temperature. 8) Repeat the experiment for all 3 alkanols.

Validity:
Invalid, as we assumed complete combustion occurs when incomplete may occur, not all of the heat is transferring to the can, the energy was lost to the atmosphere. Cause of differences in Theoretical and practical value

Energy loss to environment, equipment, incomplete combustion

Reliability:
Not reliable as practical has not been repeated with the same method and variables at least a minimum of 3 times.

Variables
Independent: The three alkanols
Dependent: The change in temperature of water, and change in mass of the corresponding spirit burner. Controlled: Perform in SLC and use the same apparatus, height of flame above aluminium can, same amount of water. Accuracy:

The experimental design is inaccurate due to the large loss of heat to the environment. It can be improved through: -Use more accurate equipment, eg electronic balance that measures more sig figs minimise heat lost:

1) Use container that absorbs less heat for example copper
2) Positioning the beaker so that the blue part of the flame touches the...
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