Ch. 18 Reaction Rates and Equilibrium Ch Rates of Reaction

Collision Theory of Rx Colliding atoms, ions, and molecules can react to form products when have enough kinetic energy. Colliding atoms, ions, and molecules can react to form products when have enough kinetic energy. If kinetic energy is too low, they bounce apart w/o reacting. If kinetic energy is too low, they bounce apart w/o reacting.

Reaction Rate Some reactions are rapid (combustion of gasoline) while others are slow (rusting of iron). Some reactions are rapid (combustion of gasoline) while others are slow (rusting of iron). The reaction rate is usually expressed as the amount of reactant changing per unit time. The reaction rate is usually expressed as the amount of reactant changing per unit time. Activation energy—the minimum energy that colliding particles must have in order to react (ex: burning match) Activation energy—the minimum energy that colliding particles must have in order to react (ex: burning match)

Factors Affecting Reaction Rates 1. Temperature—higher temperature higher Rx rate (higher kinetic energy!) 1. Temperature—higher temperature higher Rx rate (higher kinetic energy!) 2. Concentration—higher concentration of reactants, the higher the Rx rate (more collisions) 2. Concentration—higher concentration of reactants, the higher the Rx rate (more collisions) 3. Particle size—the smaller the particle size the faster the Rx rate: more surface 3. Particle size—the smaller the particle size the faster the Rx rate: more surface

4. Catalysts—speed up Rx rate, but are not consumed or do not influence enthalpy – they lower the activation energy and are written above the arrow. 4. Catalysts—speed up Rx rate, but are not consumed or do not influence enthalpy – they lower the activation energy and are written above the arrow. 5. Inhibitors –slow down/stop a Rx rate – substances that interfere with catalysts. 5. Inhibitors –slow down/stop a Rx rate – substances that interfere with catalysts.

Effect of Catalyst on Activation Energy

Activated Complex Unstable arrangement of atoms forming the transition state. It’s the top of the “hump” in the reaction curve, before they transform into products Unstable arrangement of atoms forming the transition state. It’s the top of the “hump” in the reaction curve, before they transform into products