A-Level/ Advanced Higher Chemistry course notes. Concise notes covering reaction feasibility. Notes include a clear and easy to follow summary of the topic, highlighted key-points, and supporting examples where appropriate.
REACTION FEASIBILITY
STANDARD ENTHALPY OF FORMATION
The enthalpy change OH for the reaction R P is given
by OH Hp Hr
To
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The standard state of a substance is its most stable state at a pressure of
1 atmosphere and at a specified temperature usually taken at 298 K
It follows from the above definition that the standard enthalpy
of formation of an element in its most stable form is zero
The standard enthalpy of a reaction can be calculated from the standard
enthalpies of formation of the reactants and products
H Hofproducts Hofreactants
Enthalpy is measured in kJmol
example question
calculate the standard enthalpy change for the reaction
4NH 4NO cg 6H20cal
ig 702cg
given that the standard enthalpies of formation of NH g NO cg and
HOci are 46 4 and 286 kJ mol respectively
ΔH 4 34 6 286 4 46 7 0
8H 1396 KT Mot
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