Mg(s) + ½ O2(g)  MgO(s) H = ? kJ/mol Thermochemistry Lab Calculations Goal: What is H for the formation of MgO from Mg(s) and O2(g)? Mg(s) + ½ O2(g)  MgO(s) H = ? kJ/mol Data: From lab measurements: Mg(s) + 2 H+(aq)  Mg2+(aq) + H2(g) H1 = ___________ kJ/mol MgO(s) + 2 H+(aq)  Mg2+(aq) + H2O(l) H2 = ___________ kJ/mol From a table: H2(g) + ½ O2(g)  H2O(l) H3 = -285.8 kJ/mol Task: Find a way to add these three reactions to get the desired reaction. Manipulate the H values as needed, and add them.

Given: Pb(s) + PbO2(s) + 2H2SO4(l) → 2PbSO4(s) + 2H2O(l); ∆H° = –509.2 kJ SO3(g) + H2O(l) → H2SO4(l); ∆H° = –130. kJ determine ∆H° for the following thermochemical equation. Pb(s) + PbO2(s) + 2SO3(g) → 2PbSO4(s) a) –3.77 × 103 kJ b) 3.77 × 103 kJ c) –639 kJ d) –521 kJ e) –769 kJ

Calculating Heat Production

Heat of Formation

Heat of Formation: The general idea

Find the enthalpy change for burning ethyl alcohol

What is the standard enthalpy change for the following reaction? N2H4(l) + 2NO2(g) → 2N2O(g) + 2H2O(l) a) –119.7 kJ b) –290.6 kJ c) +290.6 kJ d) –524.2 kJ e) +119.7 kJ Substance ∆H°f (kJ/mol) N2H4(l) +50.6 NO2(g) +33.1 N2O(g) +82.1 H2O(l) –285.8