Stoichiometry and Thermochemical Reactions

the energy of a reaction is directly related to the quantity of products if 28.4 kJ of energy is required to melt 1 mol of NaCl at its melting point then it would require twice that amount (56.8 kJ) to melt 2 mol of NaCl FORMULA:Q = nΔH Ex) Given: The molar heat of fusion (Δ H fusion ) for sodium = 2.63 kJ/mol a)How many kJ are required to melt 3 moles of sodium at its melting point? Q = n ΔHQ = (3 mol)(2.63kJ/mol) = 7.89 kJ

b)How many kJ are required to melt 11.5 g of sodium at its melting point? Q = n ΔH n= m/M = (11.5 g)/(22.99 g/mol) = 0.5 mol Q = n ΔH = (0.5 mol)(2.63 kJ/mol) = 1.32 kJ

Ex. Aluminum reacts readily with chlorine gas to produce aluminum chloride. The molar enthalpy of this reaction is ΔHº rxn = kJ/mol. What is the enthalpy change when 1.0 kg of Al reacts completely with excess Cl 2 ? Therefore the enthalpy change is -2.6 x 10 4 kJ. 2Al (s) + 3Cl 2(g)  2AlCl 3 (s) kJ nmMQnmMQ mol mol 1000 g g/mol 2.6 x 10 4 kJ Q = nΔH

HOMEWORK p226 #1-4 WS “Thermochemical Equations and Stoichiometry”