1. Hess’s Law
If you add two or more thermochemical equations to give a final equation, then you can also add the heats of reaction to give the final heat of reaction.
Allows you to determine the heat of reaction.

2. Manipulations
If you reverse a reaction, change the sign of ΔH.
C + O2  CO2(g) = kJ
CO2(g)  C + O2 = 393.5kJ

3. Manipulations
If you double/triple/etc. a reaction, you also must double/triple/etc. ΔH.
C + O2  CO2(g) = kJ
2C +2O2  2CO2(g) = 2*-393.5kJ

4. 4NH3(g) + 3O2(g) --> 2N2(g) + 6H2O(l)
Example
Work backwards…
Given the following, calculate ∆H for
4NH3(g) + 3O2(g) --> 2N2(g) + 6H2O(l)
2N2O(g) --> O2(g) + 2N2(g) ∆H = -164kJ
2NH3(g) + 3N2O(g) --> 4N2(g) + 3H2O(l) ∆H = -1012kJ
Answer: kJ

5. Standard Enthalpy of Formation
Represented by ∆H°f
Sometimes calorimeters can not be used to find ∆H (like if the process is very slow)
Shows how much energy is required to make 1 mole of a compound from its elements with all substances in their standard state
Table 6.2 in your book

6. Standard State Definition
COMPOUND:
Pressure = 1 atm
Pure liquid or solid
If in solution, concentration = 1M
ELEMENT:
Temperature = 25°C
State = whatever state it exists in these conditions

7. DH0reaction =∑npDHf0(products)–∑nrDHf0(reactants)
Calculating
DH0reaction =∑npDHf0(products)–∑nrDHf0(reactants)
∑ means sum of…
np is moles of product…nr is moles of reactant
If dealing with an element, the DHf0 is zero

8. CH4(g) + 2O2(g)  CO2(g) +2H2O(l)
Example
Calculate the change in enthalpy:
CH4(g) + 2O2(g)  CO2(g) +2H2O(l)
Answer:
Products: [-393.5kJ + 2(-285.8kJ)]=
-965.1kJ
Reactants: [-74.86kJ + 2(0.0kJ)] =
-74.86kJ
P-R = kJ-(-74.86kJ) = kJ

9. Fossil Fuels
When decayed plants are burned, the energy stored in them can be used
Petroleum and natural gas (hydrocarbons)
Coal: creates about 23% of U.S. energy

10. Hydrocarbons Prefixes are the same in organic chemistry Meth- Eth-
Prop-
But-
Pent-
Hex-
Hept-
Oct-
Suffixes represent different bonding/compounds

11. Environmental Impacts
Greenhouse effect: CO2 created from combustion of fossil fuels absorbs infrared radiation given off by the earth and does not allow it to leave the atmosphere
H2O can also absorb radiation (humidity), but earth’s H2O has not changed much…

12. New Energy Sources
Coal gasification: creates a gaseous form of coal (syngas) that is easily transported and reacted with oxygen in a combustion reaction, releasing energy
This material can be used to produce other fuels like methanol

13. New Energy Sources
Coal Slurries: coal ground up and mixed with water and used instead of solid coal in power plants