6.2 Calculation of enthalpy changes
6.2.1 Calculate the heat change when the temperature of a pure substance is altered.
16.1 Temperature Change and Heat (p. 627  638 McGraw-Hill Ryerson)
SPECIFIC HEAT CAPACITY (c) the amount of energy required to raise the temperature of one gram of a
substance by one Celsius degree.
Water has a high specific heat capacity (c = 4.18 J g-1 °C-1) absorbs a lot of energy, small "T
Iron has a high specific heat capacity (c = 0.45 J g-1 °C-1) small amount of energy big "T
change in energy = mass x specific heat capacity x change in temperature Q = m c "T
Practice Problems #1  4 p. 634, # 5  10 p. 636 (specific heat capacity)
6.2.2 Explain that enthalpy changes of reaction relate to specific quantities of either reactants or products.
16.2 Enthalpy Changes (p. 639  650 McGraw-Hill Ryerson)
Enthalpy changes ("H) are related to the number of moles in the reaction
If all the coefficients are doubled, then the value of "H will be doubled (*limiting reagents*).
MOLAR ENTHALPY Enthalpy changes ("H) are related to the number of moles of the limiting reagent.
Doubling the amount of the limiting reagent will double the heat gained or lost.
Thermochemical Equations - a balanced chemical equation that indicates the change in heat.
Generally given in terms of 1 mol of the limiting reagent.
żðSTANDARD MOLAR ENTHALPY OF FORMATION ("H° ) p.642
f
Ä…ð the amoiunt of energy gained or lost when one mole of a compound is formed directly from its elements in
their standard states. Standard state = common form at SATP (25°C, 101.3 kPa)
ex. carbon dioxide C(s) + O (g) Ä…ð CO (g) "H° = -393.5 kJ/mol
2 2 f
glucose 6 C(s) + 6 H (g) + 3O (g) Ä…ð C H O (s) "H° = -1274.5 kJ/mol
2 2 6 12 6 f
żðSTANDARD MOLAR ENTHALPY OF COMBUSTION ("H° ) p. 643
comb
Ä…ð the enthalpy change for the combustion of 1 mole of the given substance. Oxygen is in excess.
CH (g) + O (g) Ä…ð CO (g) + H O (l) "H° = -965.1 kJ
4 2 2 2 comb
ØðPractice Problems # 15  23 p. 643, 645 (answers on p.659)
żðEnthalpy changes and changes of state p. 645  647
ØðPractice Problems # 24  29 (omit 27) p. 648, 649 (answers on p.659)