Chapter 4 (CIC) and Chapter 5, 8 (CTCS)

• Read in CTCS Chapter 5.1,3-4, 8.9

• Problems in CTCS: 5.3, 13, 15, 22, 23, 29, 35, 90, and 8.63, 65, 67, 69

Global Warming (CO2) Fuel• Fuel’s are typically fossil fuels (crude oil, coal)

• Gasohol is a mixture of ethanol and gasolineCH2=CH2 + H2O CH3CH2OH

C6H12O6 CH3CH2OH + CO2

• Does EtOH give same performance as gasoline? Does EtOH give the same amount of energy per gram?

• 1st Law – If we have Conservation of Energy, why are worried about depleting our resources?

Annual US Energy Consumption From Various Sources

Combustion• All but two of those energy sources were based

on combustion giving CO2 as a byproduct• Energies can be obtained from a calorimeterQ: Determine the heat of combustion for a gram

of natural gas (CH4) compared to a gram of butane (C4H10) if their heats of combustion are –802.3 and –2658.4 kJ/mol respectively.

A:-50.01 kJ/g and –45.74kJ/g

Energy Diagram

Reactants

ProductsEnt

halp

y

Reaction Progress

Hrxn

• Where does the exothermic energy come from?

• When bonds are broken, energy is required• When bonds are made, energy is released• Compare the bond strengths in the equation

above (See Table 8.4 - pg 289)• The products are:

– More stable– Lower in Energy– Have stronger bonds

H

CH

H

+ 2O O O C O O2H HH +

• CO2 and H2O are too stable (have bonds that are too strong) to decompose and give off more energy

Q: Could you use ozone as a fuel? How much energy is released/g of ozone? (Use bond energies to calculate)

A: -2.11 J/g (-2.96 kJ/g according to Hºf)

• Bond Energies are averages of gas moleculesHºf – enthalpy of formation in standard state (º)

Q: Using bond energies, calculate the heat of reaction for the combustion of molecular hydrogen and 1 mol of oxygen to form gaseous products

A: -485 kJ (actual = -483.6 kJ)

Q: Would you expect a more endo- or exo-thermic reaction if the products were liquid?

• H2O(g) H2O(l) H = negative,WHY?

• 2 H2(g) + O2(g) 2 H2O(l)

• Can’t use bond energies!Hºrxn = -571.7 kJ

• Spontaneity (G)– If you have a large negative H, you can assume

spontaneity

Q: What are some of the strongest bonds?

• Triple: NN, CO; Double: C=O; Single: O-H, Si-O

• This suggests that these bonds would have trouble reacting

2 CO + O=O 2 O=C=O Hºrxn= -566 kJ

• Explosives– Should have many weak bonds– Ideally have all atoms of reaction self contained– Need to be stable enough to work with– Should create gaseous molecules

• Nitroglycerin

• What are the products of decomposition?

Q: What is the Hrxn/mol of nitro? (why not Hºrxn?)

A: -1782 kJ

CH2 O

HC

CH2

O

O

NO2

NO2

NO2