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Enthalpy Changes

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by

Simon Cunningham

on 18 April 2017

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Transcript of Enthalpy Changes

Definition
Enthalpy - The amount of heat energy extracted or absorbed in a chemical reaction.
Δ
H

Aims and Objectives :
Standard Conditions
The normal conditions required when considering enthalpy changes
Standard Enthalpy Changes
Whenever we are considering a standard enthalpy change we use the symbol Δ

Enthalpy Changes
Physical Chemistry
A visual representation of this process
Standard Enthalpy of Combustion
The standard enthalpy of combustion is the enthalpy change that occurs when one mole of a compound is burned completely in oxygen under standard conditions
Standard Enthalpy of Formation
The standard enthalpy of formation is the enthalpy change that occurs when 1 mole of a compound is formed from its constituent elements under standard conditions.
Hess's Law
"The enthalpy change accompanying a chemical change is independent of the route by which the chemical change occurs"
- To know the terminology used to describe enthalpy changes.
- To write standard enthalpy of formation and combustion equations correctly.
- To apply Hess's Law to problems involving enthalpy changes.
We represent changes in enthalpy with the symbol - Δ
H
Δ means change in
H
is our symbol for enthalpy
Temperature = 298 K (or 25 °C)
Pressure = 100 kPa (or 1 bar)
All substances must be in their standard states
All solutions have a concentration of 1 mol dm
-3
For a reaction we add a subscript Δ

r
Using the Enthalpy of Formation
Using the Enthalpy of Combustion
Full transcript