Chem 3 S2

• Chemical kinetics is the study of the rates of chemical reactions, the factors that affect these rates, and the reaction mechanisms by which reactions occur.
• Industrially important:

  1. Time
  2. Optimum yield
  3. Optimum condition (control over reaction, obtain product, economically )
• rate = -d[A]/Dr

  rate = d[B]/dt

  
• Average rate is the rate over a period of time.
• Instantaneous rate is the rate of reaction at a given time.
• Initial rate is the instantaneous rate at the beginning of a reaction
• Instantaneous rate is determined from a graph of concentration vs time by drawing a line tangent to the curve at that particular time
• H2O2(aq) → H2O(l) + 1/2 O2(g)

  An average rate from the purple line.

  
• H2O2(aq) → H2O(l) + 1/2 O2(g)

  The instantaneous rate at t=300 s from the red line.

  
• H2O2(aq) → H2O(l) + 1/2 O2(g)

  The initial rate from the blue line.

  
• x= rate at specific time

  A = - d[Br2]

  B = dt

  
• x = rate of reaction

  
• x= 1/a

  y= d[A]

  
• Rate law = k[A]^x[B]^y
• The order of a reactant is not related to the stoichiometric coefficients of the reactants in the balanced chemical equation.
• Zero order, k= Ms^-1

  First order, k= s^-1

  Second order, k= M^-1s^-1
• Order of reaction - the power to which the concentration of reactant is raised in the rate equation
• Overall order of reaction - sum of the powers of the concentration terms in the rate equation
• Order of reaction MUST BE DETERMINED experimentally, no theoretical value!
• A zero order reaction is a reaction independent of the concentration of reactant
• Graph for zero order reaction

  
• Graph for zero order reaction

  
• [A initial]-[A final] = kt

  
• [A initial]/2k

  
• Graph for first order reaction

  
• x= In ([A initial]/[A])

  y= kt

  
• Graph for first order reaction

  
• Graph for first order reaction

  
• x= 1/[A]

  y= 1/[A initial] + kt

  
• Graph for second order reaction

  
• Graph for second order reaction

  
• Half line second order

  z= 1/[A initial]

  
• Collision Theory is the theory to explain the rate of chemical reactions
• 1. molecule must collide to react
  2. molecules must possess a certain minimum kinetic energy (activation energy) to initiate the chemical reaction.
  3. molecule must collide in the right orientation in order for the reaction to occur.
• The activation energy (E) is the minimum energy that must be supplied or required by collisions for a reaction to occur.
• Exothermic reaction

  
• Endothermic reaction

  
• Concentration of reaction increase

  The frequency of collision increase

  The rate of effective collision increase

  The rate of reaction increase
• Temperature increase

  Kinetic energy increase

  The frequency of collision increase

  The rate of effective collision increase

  The rate of reaction increase
• Size of particles decrease

  Total surface area exposed increase The frequency of collision increase The rate of effective collision increase The rate of reaction increase