1. DO NOW: On back of Notes!
How much heat (in kJ) is given out when 85.0g of lead cools from 200.0C to 10.0C? (c=.129 J/gC)

2. Unit: Thermochemistry
Notes
Unit: Thermochemistry
Thermochemical Equations

3. After today you will be able to…
Define what a thermochemical equation is and use its information to calculate the energy used or produced in a chemical reaction
Explain what the ΔH of a reaction is and how it can be found

4. Thermochemical equation: A chemical equation which includes the energy used or produced in a chemical reaction. (Every reaction has an energy change associated!)

5. Enthalpy: (H) Heat content of a substance at constant pressure.
“Heat of a reaction” - heat that is absorbed or released during a chemical reaction
ΔH= change in enthalpy

6. Exothermic Reactions can be shown two ways:
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) ΔH= kJ CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) kJ
Negative sign means the reaction is exothermic!
Energy is a product in an exothermic reaction!

7. Endothermic Reactions can be shown two ways:
C(s) + 2S(s)  CS2(l) ΔH= +89.3kJ C(s) + 2S(s) kJ  CS2(l)
Positive sign means the reaction is endothermic!
Energy is a reactant in an endothermic reaction!

8. NEW conversion factor:
The heat of a reaction (ΔH) is the amount of energy used or produced when the coefficient equals the number of moles in a reaction. Coefficient of any substance = ΔH
NEW conversion factor:

9. Examples
How much energy is needed when 1.27 moles of sulfur reacts with excess carbon? C(s) + 2S(s)  CS2(l) ΔH= +89.3kJ 1.27 mol S x __________ =
K: 1.27 mol S
U: ? kJ kJ
+56.7kJ
2 mol S

10. Examples
How many moles of water would be produced if this reaction gave off 347.1kJ of energy? CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) kJ kJ x __________ =
K: kJ
U: ? mol H2O
2 mol H2O
mol H2O kJ

11. C2H5OH(l) + 3O2(g)  2CO2(l) + 3H2O(g) + 1235kJ
How much energy is produced when 75.0g of oxygen reacts with excess ethanol (C2H5OH)?
C2H5OH(l) + 3O2(g)  2CO2(l) + 3H2O(g) kJ
75.0gO2 x _________ x _________=
K: 75.0 gO2
U: ? kJ
1 mol O2
-1235kJ
-965kJ
32.00gO2
3 mol O2

12. Questions? Complete WS

13. SILENCE IS GOLD-EN