Progress of Chemical Reactions

Rate Laws An expression for the rate of a reaction in terms of the concentrations of the reactants Equation: A  B rate = k[A] k is a constant

Rate Constant Specific rate constant (k): a proportionality constant relating the concentration of the reactants to the reaction rate k is large is the products form quickly k is small is the products form slowly

Order of Reaction First order reactions: the reaction rate is directly proportional to the concentration of one reactant The exponent for that reactant is 1 Half the concentration, half the rate Rate = k[A][B] Reaction is first order in A and B

First Order Reaction

Order of Reactions Reactions can be second or third order, with the reactants raised to the power of 2 & 3 respectively. Order of reaction is determined experimentally. 9 out of 10: coefficient will be the exponent aA + bB  cC rate = [A]a[B]b Overall order of the reaction is the sum of the exponents for the individual reactants 2N2O  2N2 + O2 rate = [N2O]2 Overall order: 2 2N2 + O2  2N2O rate = [N2]2[O2] Overall order: 3

Second Order Reactions

Reaction Mechanisms Elementary Rxn: Reactants Products in 1 step 1 activation energy peak Reaction Mechanism: series of elementary reactions Reaction progress is a series of peaks and valley Peaks: activation energy Valley: energy of intermediates Intermediate: product of the steps in the reaction mechanism N2O  N2 + O N2O + O  N2 + O2 2N2O  2N2 +O2

Reaction Mechanisms

Reaction Mechanism