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The Enthalpy Change of Combustion

The standard enthalpy change of combustion is defined as: The enthalpy change when one mole of a substance in its standard state burns completely in oxygen under standard conditions of 298K and 100kPa pressure.For the formation of ethanol:2C(s) + 3H2(g) + ½O2(g) → C2H5OH(l)the elements and ethanol both burn to give the same products, 2CO2(g) + 3H2O(l), so by Hess's law ΔHf = 2ΔHc(carbon) + 3ΔHc (hydrogen) - ΔHc(ethanol)

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Specification: AQA Chemistry (7404), AS-level, 3.1.4.1 Enthalpy change. Topic: Energetics.

Key terms in this lesson

Mole
The amount of substance that contains as many particles as there are atoms in exactly 12g of carbon-12.
Enthalpy
A measure of the heat energy stored in a chemical system.
Enthalpy change
The heat energy transferred between the system and its surroundings during a process carried out at constant pressure.
Standard conditions
A pressure of 100 kPa, a temperature of 298 K, and, for solutions, a concentration of 1 moldm-3.

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