1. Formation Reactions Examples: C (s) + O 2(g)  CO 2(g) Na (s) + ½ Br 2(l)  NaBr (s) 6C (s) + 6H 2(g) + 3O 2(g)  C 6 H 12 O 6(s)

2. Formation Reactions The formation of 1 mole of a substance from its elements in their standard state – i.e. their most stable form at SATP – (what they are on the periodic table)

3. Write the formation reaction for: Sodium hydroxide Na (s) + ½ O 2(g) + ½ H 2(g)  NaOH (s) Aluminum phosphate Al (s) + P (s) + 2O 2(g)  AlPO 4(s) Potassium bromate K (s) + Br 2(l) + 3/2 O 2(g)  KBrO 3(s)

4. Standard Enthalpy of Formation ΔH f o The energy associated with a formation reaction Units: kJ/mol Enthalpy of formation of an element already in its standard state i.e. O 2(g) = zero

5. Look up the ΔH f o for NaOH KClO 3 O 2(g) O (g) I 2(s) I 2(g) I - (aq)

6. Hess’s Law Using ΔH f o CH 4(g) + 2O 2(g)  CO 2(g) + 2H 2 O (g) 1)Write the formation reactions for each substance in the above reaction. 2)How would you rearrange each equation to make the target equation?

7. CH 4(g) + 2O 2(g)  CO 2(g) + 2H 2 O (g) C (s) + 2H 2(g)  CH 4(g) x (-1)ΔH f o x (-1) O 2(g)  O 2(g) x(-1)ΔH f o x(-1) C (s) + O 2(g)  CO 2(g) x1ΔH f o x1 H 2(g) + ½ O 2  H 2 O (g) x2ΔH f o x2

8. CH 4(g) + 2O 2(g)  CO 2(g) + 2H 2 O (g) ΔH rxn = (1)ΔH f o CO 2 + (2)ΔH f o H 2 O + (-1)ΔH f o CH 4 + (-1)ΔH f o O 2 ΔH rxn = [(1)ΔH f o CO 2 + (2)ΔH f o H 2 O] –[(1)ΔH f o CH 4 + [(1)ΔH f o O 2 ] ΔH rxn = [(n)ΔH f o CO 2 + (n)ΔH f o H 2 O] –[(n)ΔH f o CH 4 + [(n)ΔH f o O 2 ] ΔH rxn = Σn ΔH f o Products - Σn ΔH f o Reactants ΔH rxn = [-393.5 + 2(-242)] – [-75 + 2(0)] = -802.5kJ

9. ΔH rxn = Σn ΔH f o Products - Σn ΔH f o Reactants Try: 1)CH 3 OH (l) + 3O 2(g)  2CO 2(g) + 4H 2 O (l) ΔH rxn = -1692 kJ 2) 4NH 3(g) + O 2(g)  4NO 2(g) + 6H 2 O (l) ΔH rxn = -1396 kJ 3) What is the molar enthalpy of combustion of propane? ΔH rxn = -2220.5 kJ

10. 4) The standard enthalpy of combustion of liquid cyclohexane, C 6 H 12, to liquid water and carbon dioxide is -3824 kJ. What is the standard enthalpy of formation of cyclohexane? ΔH f o = -252 kJ/mol

11. Hess’s Law and Calorimetry 5) What mass of methane undergoing complete combustion is required to heat 100.0 kg of water from 5.0 o C to 70.0 o C in a gas water heater? m = 480 g

12. Hess’s Law and Calorimetry A 0.092 g sample of acetone is burned in 50.0 g aluminum calorimeter containing 100.0 g of water. The temperature rises from 20.0 o C to 25.0 o C. a)What is the molar enthalpy of combustion of acetone, C 3 H 8 O? b)Calculate the percent error.