1. Exothermic vs. Endothermic

3. Decomposition of Nitrogen Triiodide

4. Decomposition of Nitrogen Triiodide
Molecules store energy (chemical potential energy) in the bonds that hold them together. When the bonds are broken, energy is released.
2 NI3(s) N2(g) I2(g)

5. Exothermic Reaction Reactants  Products + Energy Energy Reactants -DH
10 energy = energy energy
Energy of reactants
Energy of products
Energy
Reactants
-DH
Products
Reaction Progress

6. Endothermic Reaction +DH Endothermic Energy Reaction progress
Energy + Reactants  Products
Activation
Energy
Products
Energy
+DH Endothermic
Reactants
Reaction progress

7. Effect of Catalyst on Reaction Rate
What is a catalyst? What does it do during a chemical reaction?
Catalyst lowers the activation energy for the reaction.
No catalyst
activation energy
for catalyzed reaction
reactants
Energy
A catalyst lowers the activation energy for the reaction. This allows the reaction to occur at a much faster rate.
The catalyst is not a reactant or product. It is not consumed during the chemical reaction.
products
Reaction Progress

8. Animation by Raymond Chang
An Energy Diagram
activated
complex
activation
energy Ea
reactants
products
energy
course of reaction
Animation by Raymond Chang
All rights reserved

9. Energy Sources in the United States
Wood
Coal
Petroleum / natural gas
Hydro and nuclear
1850
1900
1940
1980
1990
100 80 60 40 20
Percent 9 91 21 71 5 3 10 50 70 26 58 16
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 307

10. Energy Sources in the United States
100 80 60 40 20 91
1900 21 71 5 3
1980 20 70 10
1990 26 58 16
1940 10 50 40
Percent 9
FUELS - Energy can never actually be consumed but can be changed from one form to another.
The major reason for the huge consumption of energy is the low efficiency of most machines in transforming stored energy into work
– Efficiency is the ratio of useful work accomplished to energy expended
• It is more efficient to use primary sources of energy directly than to transform them to a secondary source.
• The total expenditure of energy in the world each year is 3 x 1017 kJ.
• More than 80% of this energy is provided by the combustion of fossil fuels: oil, coal, and natural gas.
• Natural gas and petroleum are the preferred fuels due to their availability, ease of transport, and facile conversion to convenient fuels.
1850
Wood
Coal
Petroleum / natural gas
Hydro and nuclear
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 307

11. Energy Sources in the United States
100 80 60 40 20 91
1900 21 71 5 3
1980 20 70 10
1990 26 58 16
1940 10 50 40
2005 50 21 26
Percent 9
Source: US Energy Information Administration (2005 Electricity Generation)
49.9% Coal
3.1% Renewable (biomass, geothermal, solar, wind)
6.6% Hydroelectric
2.5% Petroleum
18.8% Natural gas
19.3% Nuclear
Society requires the constant expenditure of huge amounts of energy.
The United States consumes 106 kJ per person per day or 30% of the world’s total energy usage.
1850
Wood
Coal
Petroleum / natural gas
Hydro and nuclear
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 307

12. thermal and radiant energy
Energy Conversion
fan
electrical energy to
mechanical energy
coffee maker
electrical energy to
thermal energy
light bulb
electrical energy to
light energy to
thermal and radiant energy
Energy can be converted from one form to another or transferred from one object to another.
Law of conservation of energy — total amount of energy in the universe remains constant.
Energy cannot be created or destroyed.
In each step of an energy conversion some of the usable energy is "lost" or dissipated as heat, sound or light.
pencil sharpener
electrical energy to
mechanical energy
Timberlake, Chemistry 7th Edition, page 202