1. Lesson # 5: Standard Enthalpies of Formation
Thermochemistry
Lesson # 5:
Standard Enthalpies of Formation

2. Standard States
A substance is in a standard state when it is in its most stable form at SATP (25°C, 100 kPa).
The standard enthalpy of formation, ΔH°f, of a compound is the change in enthalpy that occurs when 1 mol of a compound is formed from its elements, all in standard states.
The standard enthalpy of formation of all individual elements is zero. The rest of the enthalpies of compounds have already been determined and are listed in a table.

3. Example 1
Calculate the standard change in enthalpy for the Thermite reaction, represented by the balanced equation:
Al (s) + Fe2O3 (s) → Al2O3 (s) + 2 Fe (s)

4. Example 2A
a) Determine the standard enthalpy of reaction for the combustion reaction: CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (l)

5. Example 2B
b) Determine the standard enthalpy of combustion of methane per gram.