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NOTES: THERMOCHEMICAL EQUATIONS
A. ENTHALPY
1. Enthalpy (H) is the amount of heat in a system
2. Thermochemical Equations:
A. Endothermic (+∆H): Heat is on the left (reactants)
B. Exothermic (-∆H): Heat is on the right (products)
3. Enthalpy Types: ∆H(phase change) or ∆H(reaction)
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B. ENTHALPY STOICHIOMETRY
Example 1: Calculate the energy required to melt 250 g
of ice. (ΔHfusion = 6.01 kJ/mol) (fusion = melting)
250 g H2O x 1 mol H2O x 6.01 kJ = 83 kJ
18.02 g H2O 1 mol H2O
B. ENTHALPY STOICHIOMETRY
Example 2: How much heat is required to consume 54.0 g CO2?
endo
+2808 kJ
6 CO2 + 6H2O + 2808 kJ C6H12O6 + 6O2
ΔH= ___________
54.0 g CO2
x
1 mol CO2
44.01 g CO2
x
2808 kJ
= 574 kJ
6 mol CO2
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B. ENTHALPY STOICHIOMETRY
Determine the mass of iron used to produce 250 kJ of heat
according to the balanced reaction below. exo
-1625 kJ
4Fe + 3O2  2Fe2O3 + 1625 kJ
ΔH= ___________
-250 kJ x
4 mol Fe
-1625 kJ
x
55.85 g Fe
= 34 g Fe
1 mol Fe
Produce = - energy
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