1. Review:
If 400 kJ is required to break 1 mole of H – Cl bonds, how much is released when forming 1 mole of H – Cl bonds?
What is the net enthalpy change for the formation of HCl from hydrogen gas and chlorine gas? Include units and proper sign.
H2 + Cl2  2HCl
(H – H bond energy is 400 kJ/mol, Cl – Cl bond energy is 200 kJ/mol)

2. Enthalpy basics:
Since ∆H values are based on how many moles of bonds are broken / absorbed, they are considered stoichiometric values!!!
241.8 kJ +
1H2O(g)  1H2(g) + ½ O2(g) ∆H = kJ/mol-rxn
483.6 kJ +
2H2O(g)  2H2(g) + 1O2(g)
∆H = kJ/mol-rxn
2H2(g) + 1O2(g)  2H2O(g) kJ
∆H = kJ/mol-rxn

3. Enthalpy Stoichiometry:
Sucrose, C12H22O12 can be oxidized to CO2 and H2O and the enthalpy change can be measured under constant pressure.
2C12H22O O2  24CO H2O ∆rHo = KJ/mol-rxn
What is the energy transferred as heat by burning 5.0 g sucrose? What is the direction of this heat flow?

4. Enthalpy Stoichiometry:
The dissolution of ammonium chloride in water is an endothermic process with a solution enthalpy of 5.67 kJ/mol. How much heat will be absorbed from the surroundings if 10 grams of NH4Cl dissolves in water?

6. Challenge Problems:
3 “challenge” problems have been provided to give you some practice dealing with different stoichiometry problems
Remember the basics!!!
1. Write the balanced reaction
2. Find the LR
3. Use that LR and mole ratios to solve for anything else in the reaction the problem asks about!!!