5-21-15 Turn in nomenclature worksheet Get out notes packet on Reaction rates and chemical equilibrium

Chemical Equilibrium

Reaction Rates & Equilibrium Reaction Rate = Speed of Reaction Tells you how much of the reactants are converted to products over a period of time. Some reactions are very slow, others are very fast. Collision Theory: In order to combine chemically, the reactant particles must make contact and have enough energy. w/o enough energy  just bounce apart Activation Energy = Minimum energy colliding particles must have to react. (Barrier reactants must pass to become products)

Energy Diagrams Activated Complex  H

Energy Diagrams Activated Complex  H

H = change in energy from reactants to products - for exothermic + for endothermic Activated complex: the arrangement of atoms at the peak of the activation energy barrier. If they have enough Energy they can go over the barrier; if not, they will return to reactants. Activated complex is sometimes called the transition state. It is unstable and contains more Energy than either the reactants or products.

Factors Affecting Reaction Rates Temperature – usually speed up a reaction Higher T = particles are moving more quickly and with more energy. They are more likely to be energetic enough to slip over the activation barrier. Concentration = more particles in a given volume increases the # of collisions Particle Size = smaller particle size = larger surface area  inc. in collision frequency  inc. in rate. EX: Larger particles dissolve more slowly than finely ground particles

Factors Affecting Reaction Rates Cont. Catalyst: A catalyst is a substance that increases the rate of a reaction without being used up itself. Catalysts provide reactants with a reaction path with lower activation energy. With lower activation energy, more particles will have enough energy to cross the activation energy barrier. Inhibitor: a substance that interferes with catalysis.

 H

Energy Diagram Worksheet

Chemical Equilibrium In reversible reactions the conversion of reactants into products and the conversion of products into reactants occur at the same time. The conversion of reactants into products is the forward reaction. The conversion of the products into reactants is the reverse reaction. __ ;  shows a reaction is reversible. As the reaction proceeds, the rate at which reactants go to products becomes equal to the rate at which the products go to reactants. Chemical equilibrium is reached at that point. The concentrations of products & reactants does not change.

Vocab first, then explanation Dynamic Equilibrium – State when two opposing processes coexist at the same rate. -Think of a water fountain Equilibrium constants are used to tell whether reactants or products are favored in a reaction. For the reaction: aA + bB  cC + dD the equilibrium constant, Keq, is the ratio of the product concentrations to reactant concentrations, each concentration raised to a power given by the number of moles (coefficient) of that substance in the balanced equation.

Keq = [C]c [D]d = [products] coef [A]a [B]b [reactants] coef aA + bB  cC + dD Keq = [C]c [D]d = [products] coef [A]a [B]b [reactants] coef [ ] indicate the concentrations are in moles/L (M). The value of Keq depends on the T and changes when the T changes. Keq > 1 = products favored Keq < 1 = reactants favored Keq = 1 = neither forward or reverse is favored [R] = [P]

Guidelines for writing Keq start w/ balanced reaction Keq changes with temperature concentrations are for gases & solutes in solution. concentrations for any solid or liquid does not appear in expression.

Examples: CaCO3 (s)  Ca2+ (aq) + CO3-2(aq)

2H2 (g) + O2 (g)  2 H2O2(g)

AgCl(s)  Ag+ (aq) + Cl- (aq)

4NH3 (g) + 5O2 (g)  4 NO (g) + 6H2O (g)

Chem Equilibrium Worksheet

Turn in your worksheets from yesterday Video Quiz Notes 12/11/15