Chapter 6: Energy Changes, Reaction Rates, and Equilibrium

Chapter Objectives

  • 6.1: Differentiate potential vs kinetic energy; law of conservation of energy; caloric values from fats, carbs, proteins; nutrition labels; energy unit conversions (J, kJ, cal, Cal, kcal).

  • 6.2: Energy changes in reactions; classify reactions as endothermic or exothermic.

  • 6.3: Analyze energy diagrams (reactants, products, Ea, ΔH).

  • 6.4: Predict how concentration, temperature, and catalysts affect reaction rates.

  • 6.5: Describe chemical equilibrium and write equilibrium constant expression (Keq).

Energy Basics (6.1)

  • Energy: Capability to perform work.

  • Kinetic Energy: Energy of motion.

  • Potential Energy: Stored energy in chemical bonds.

  • Law of Conservation of Energy: Energy cannot be created or destroyed, only transformed.

Units of Energy

  • calorie (cal): Energy to raise 1g water by 1°C.

  • Conversions: 1 cal = 4.184 J; 1 kcal = 1000 cal = 4.184 kJ.

Energy Changes in Reactions (6.2)

  • Bonds in reactants are broken, new bonds in products formed.

  • Breaking bonds requires energy; bond formation releases energy.

  • Heat of Reaction (ΔH): Positive for endothermic (absorbs heat) and negative for exothermic (releases heat).

Energy Diagrams (6.3)

  • Activation Energy (Ea): Minimum energy needed for a reaction.

  • Energy diagrams show changes in energy and the transition state where reactants form products.

  • ΔH indicates heat of reaction; positive if products need more energy than reactants (endothermic), negative if vice versa (exothermic).

Reaction Rates (6.4)

  • Higher Ea slows reactions, lower Ea speeds them up.

  • Factors influencing rate: Concentration (↑ concentration = ↑ collision rate), Temperature (↑ temperature = ↑ kinetic energy), Catalysts (lower Ea, not consumed).

Chemical Equilibrium (6.5)

  • Equilibrium: Rate of forward reaction equals rate of reverse reaction.

  • Equilibrium constant (K) relates to concentration of products and reactants; K>1 favors products, K<1 favors reactants.

  • Changes in conditions can affect equilibrium but will revert to balance.