CO4

• Chemical Kinetics

  study of the rates of chemical reactions
• Macroscopic Level

  what reaction rate means

  how to determine a reaction rate experimentally

  how factors influence rates
• Particulate Level

  reaction mechanism

  detailed pathway taken by atoms and molecules as a reaction proceeds
• Rate of Chemical Reaction

  change in concentration of a reactant or product per unit of time.
• Average Rate of Reaction

  a change in concentration divided by a change in time from the chosen time interval
• Instantaneous Rate of Reaction

  the slope of a line tangent to the concentration-time curve at the point corresponding to the specified concentration and time.
• Factors that Affect Reaction Rates

  Physical State of the Reactants

  Concentration of Reactants

  Temperature

  Presence of a Catalyst
• Physical State of the Reactants

  more homogeneous the mixture = faster the reaction
• Concentration of Reactants

  increasing concentration = increasing likelihood of molecules collision
• Temperature

  higher temperature = higher kinetic energy = faster movement = higher collision
• Presence of a Catalyst

  Catalyst speed up reactions by changing the mechanism of the reaction

  Not consumed during the course of the reaction
• Rates of Reaction

  determined by monitoring the change in concentration of either reactants or products as a function of time
• As the reaction goes forward, there are fewer collisions between reactant molecules
• Slope of a line tangent to the curve at any point is the instantaneous rate at that time.
• Best Indicator of the Rate of a Reaction

  Instantaneous rate near the beginning of the reaction.
• The Rate Law

  relationship between the rate of a reaction and the concentrations of reactants
• Collision Theory

  Three conditions:

  reacting molecules must collide with one another

  reacting molecules must collide with sufficient energy to initiate the process of breaking and forming bonds

  molecules must collide in an orientation that can lead to rearrangement of the atoms and the formation of products
• Concentration and Reaction Rate

  number of collisions between the two reactant molecules is directly proportional to the concentration of each reactant

  Increasing the concentration, increases the number of collisions, thus increasing the rate of reaction
• Activation Energy

  Molecules require some minimum energy or energy barrier to react

  High Barrier = High Activation Energy = Few Reactant Molecules = Slow Reaction

  Energy of the system reaches a maximum at the transition state
• Activation Energy and Temperature

  Raising the temperature increases the reaction rate by increasing the fraction of molecules with enough energy to surmount the activation energy barrier

  High Temperature = Fast Reaction Rate = Increased fraction of molecules
• Effect of Molecular Orientation on Reaction Rate

  Reactants must also come together in the correct orientation for a reaction to occur

  Low probability of achieving proper alignment = Smaller value of k = Slower reaction

  fractional factor is called steric factor
• Arrhenius Equation

  can be used to calculate Ea from the temperature dependence of the rate constant

  can be used to calculate the rate constant, if Ea , T, and A are known
• Effect of Catalysts on Reaction Rate

  Catalyst - substance that speeds up (or slows down) the rate of a chemical reaction

  not consumed in a chemical reaction

  function is to provide a different pathway with a lower activation energy for the reaction
• Catalyst

  rate catalyzed > rate uncatalyzed
• Types of Catalysis

  Homogeneous - same physical state

  Heterogeneous - difference physical state

  Enzyme - biomolecules
• Homogeneous Catalysis

  Reactants and catalyst are in similar phases
• Enzymes

  Biological catalysts that are highly specific

  Substrates - enzyme acts only on certain molecules
• Glycolysis

  first step in the breakdown of glucose to extract energy for cellular metabolism

  consists of an energy-requiring phase followed by an energy-releasing phase