# Energetics

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• Created by: sydjow17
• Created on: 08-12-19 15:28

## Determination of enthalpy change of combustion.

The method to determine the enthalpy of combustion of a fuel such as ethanol or methanol is as follows:

- accurately measure 100cm^3 of water into a calorimeter/beaker. (100cm^3 of water is the same as 100g of water as the density of water is 1g/cm^3).

- weigh a spirit burner containing the liquid to be burnt.

- measure the initial temperature of the water using a thermometer (T1).

- use the spirit burner to heat the water.

-stop heating when there is a reasonable temperature rise (15˚c). Stir and measure the final temperature (T2) of the water using a thermometer.

-reweigh the spirit burner.

- calculate the temperature change, and the heat energy change.

- calculate the mass of fuel used, and then the moles of fuel used.

- calculate the energy change per mole of fuel used.

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## Experimentally determined enthalpy of combustion.

The value for the enthalpy of combustion determined experimentally is frequently lower than the value found in data books. Reasons for this are:

- heat losses to the surroundings from the spirit burner, wick and calorimeter.

- loss of fuel from the wick or burner, by evaporation.

- loss of water by evaporation.

- incomplete combustion of fuel.

- heat used to raise the temperature of the calorimeter.

- the reaction is unlikely to occur under standard condiitons.

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