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 Form 4 Chemistry: Energy changes in chemical and physical processes lessons

Standard conditions for measuring enthalpy changes.

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Answer Text:
Standard conditions for measuring enthalpy changes.
- Experimental evidence shows that enthalpy changes are affected by physical stats of the reactants, temperature, concentration and pressure.
- Consequently, for comparison purposes certain conditions have been chosen as standard for measurement and determination of enthalpy
changes.
- These conditions are:
-A temperature of #25^0C# (298K)
-Pressure of 1 atmosphere (101.325K)
Standard enthalpy changes:
- Are values of enthalpy changes that are measured under standard conditions.
- They are denoted by the symbol ΔH0
figenergy25720201002.JPG
- A subscript is also added to the symbol to indicate the type of enthalpy change involved.