1. Formation Reactions Examples: C(s) + O2(g)  CO2(g)
Na(s) + ½ Br2(l)  NaBr(s)
6C(s) + 6H2(g) + 3O2(g)  C6H12O6(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 O2(g) + ½ H2(g)  NaOH(s) Aluminum phosphate Al(s) + P(s) + 2O2(g)  AlPO4(s) Potassium bromate K(s) + Br2(l) + 3/2 O2(g)  KBrO3(s)

4. Standard Enthalpy of Formation ΔHfo
The energy associated with a formation reaction
Units: kJ/mol
Enthalpy of formation of an element already in its standard state i.e. O2(g)
= zero

5. Look up the ΔHfo for
NaOH
KClO3
O2(g)
O(g)
I2(s)
I2(g)
I-(aq)

6. CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
Hess’s Law Using ΔHfo
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
Write the formation reactions for each substance in the above reaction.
How would you rearrange each equation to make the target equation?

7. CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
C(s) + 2H2(g)  CH4(g) x (-1) ΔHfo x (-1) O2(g)  O2(g) x(-1) ΔHfo x(-1) C(s) + O2(g)  CO2(g) x1 ΔHfo x1 H2(g) + ½ O2  H2O(g) x2 ΔHfo x2

8. CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
ΔHrxn = (1)ΔHfo CO2 + (2)ΔHfo H2O + (-1)ΔHfo CH4 + (-1)ΔHfo O2
ΔHrxn = [(1)ΔHfo CO2 + (2)ΔHfo H2O] –[(1)ΔHfo CH4 + [(1)ΔHfo O2]
ΔHrxn = [(n)ΔHfo CO2 + (n)ΔHfo H2O] –[(n)ΔHfo CH4 + [(n)ΔHfo O2]
ΔHrxn = Σn ΔHfo Products - Σn ΔHfo Reactants
ΔHrxn = [ (-242)] – [ (0)]
= kJ

9. ΔHrxn = Σn ΔHfo Products - Σn ΔHfo Reactants
Try:
CH3OH(l) + 3O2(g)  2CO2(g) + 4H2O(l)
ΔHrxn = kJ
2) 4NH3(g) + O2(g)  4NO2(g) + 6H2O(l)
ΔHrxn = kJ
3) What is the molar enthalpy of combustion of propane?
ΔHrxn = kJ

10. 4) The standard enthalpy of combustion of liquid cyclohexane, C6H12, to liquid water and carbon dioxide is kJ. What is the standard enthalpy of formation of cyclohexane?
ΔHfo = -252 kJ/mol

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

12. Hess’s Law and Calorimetry
A g sample of acetone is burned in 50.0 g aluminum calorimeter containing g of water. The temperature rises from 20.0 oC to 25.0oC.
What is the molar enthalpy of combustion of acetone, C3H8O?
Calculate the percent error.