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2. Hess’s Law Due to first law and H being a state function.
If a reaction is reversed, the sign of H is also reversed
The magnitude of ΔH is directly proportional to the quantities of reactants and products in a reaction.
That is, if the coefficients in a balanced equation are multiplied by an integer, the value of H is multiplied by the same integer.

3. 2NaHCO3(s)  Na2CO3(s) + CO2(g) + H2O(l)
Clicker Question
Baking soda can decompose to produce sodium carbonate, carbon dioxide, and water according to the following chemical equation:
2NaHCO3(s)  Na2CO3(s) + CO2(g) + H2O(l)
Given the following data, determine ΔH° for the decomposition of baking soda as written above.
Na2CO3(s) + 2HCl(aq)  2NaCl(aq) + CO2(g) + H2O(l) ΔH° = –28.9 kJ/mol
NaHCO3(s) + HCl(aq)  NaCl(aq) + CO2(g) + H2O(l) ΔH° = 28.3 kJ/mol
a) –0.6 kJ b) kJ c) kJ d) kJ e) kJ

4. Chapter 9: Problem #117
This problem is an application of Hess’s law, although it may not be obvious upon reading it.

5. Clicker Question
Using the following data, calculate the standard enthalpy of formation of the compound ICl(g), in kJ/mol:
H° (kJ/mol)
Cl2(g)  2Cl(g) 242.3
I2 (g)  2I(g) 151.0
ICl(g)  I(g) + Cl(g) 211.3
I2(g)  I2(s) –62.8
a) –14.6 b) – c) – d) e) 33.5

6. Fe2O3(s) + 2Al(s)  Al2O3(s) + 2Fe(l)
Clicker Question
Given that ΔH°fusion for Fe(s) = 13.6 kJ/mol and the following data:
Fe2O3(s) Al2O3(s)
ΔHf°(kJ/mol) –826.0 –1676.0
Determine ΔH°rxn (kJ) for the thermite reaction (at constant temperature) as represented by the equation:
Fe2O3(s) + 2Al(s)  Al2O3(s) + 2Fe(l)
a) – b) – c) – d) – e) –877.2