Exothermic vs. Endothermic http://www.dnr.state.wi.us/org/es/science/lc/OUTREACH/BODresource/images%5Csnowman.gif

Decomposition of Nitrogen Triiodide

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) + 3 I2(g)

Exothermic Reaction Reactants  Products + Energy Energy Reactants -DH 10 energy = 8 energy + 2 energy Energy of reactants Energy of products Energy Reactants -DH Products Reaction Progress

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

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

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

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

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

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

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