1. Method 1: Molar Enthalpies of Reaction, ΔrHm
When reactants and products are in their standard state, they are at a pressure of 100 kPa, an aqueous concentration of 1.0 mol/L & liquids and solids are in their pure state.
To communicate a molar enthalpy, both the substance & the reaction must be specified.

2. Formation Reaction
Combustion Reaction
Note that the above reactions are balanced for one mole of the compound.

3. Δf Hm° = –239.2 kJ/mol Δc Hm° = –725.9 kJ/mol Formation Reaction
CH3OH
When 1 mol of methanol is formed from its elements when they are in their standard states at SATP, kJ of energy is released.
Combustion Reaction
Δc Hm° = –725.9 kJ/mol
CH3OH
The complete combustion of 1 mol of methanol releases kJ of energy.
Note that the above reactions are balanced for one mole of the compound.

4. Method 2: Enthalpy Changes, ΔrH
Write an enthalpy change (Δr H) beside the chemical equation.
CO(g) + 2 H2(g) → CH3OH(l)
Δr H = –725.9 kJ
The enthalpy change is not a molar value, so does not require the “m” subscript and is not in kJ/mol.
Δc H° = –98.9 kJ
Δc H° = –197.8 kJ
When 2 moles of sulfur dioxide are burned, twice as much heat energy is released as when 1 mole of sulfur dioxide is burned.

7. Method 3: Energy Terms in Balanced Equations
For endothermic reactions, the energy is listed along with the reactants.
reactants + energy → products
For exothermic reactions, the energy is listed along with the products.
reactants → products + energy

9. Method 4: Chemical Potential Energy Diagrams
During an exothermic reaction, the enthalpy of the system decreases. Heat flows out of the system and into the surroundings & we observe a temperature increase.

10. Method 4: Chemical Potential Energy Diagrams
During an endothermic reaction, the enthalpy of the system increases. Heat flows into the system from the surroundings & we observe a temperature decrease.

14. Summary

15. Homework:
Read pgs. 495 – 500
Section 11.3 Questions #’s 1, 3, 4, 5 (p. 501)