Kinetics pdf

• What area of chemistry concerns reaction rates?

  Chemical kinetics
• What are spontaneous reactions?

  Reactions that will happen, but speed is unknown
• How is reaction rate defined?

  Change in concentration per unit time
• What is the formula for calculating reaction rate?

  Rate = (conc. of A at t2 - conc. of A at t1) / (t2 - t1)
• What happens to the concentration of N₂ in the reaction 2 N₂ + 3 H₂ → 2 NH₃ as it progresses?

  It decreases at a rate of 1/3
• What is the difference between average rate and instantaneous rate?

  Average rate is over long intervals; instantaneous is at a point
• What is the significance of the initial rate method?

  Measurements are taken as soon as reactants are mixed
• What does the rate law express?

  How rate depends on concentration
• Why do products not appear in the rate law?

  Because the reverse reaction does not contribute
• What must be determined experimentally in rate laws?

  The value of the exponent n
• What are the two types of rate laws?

  • Differential Rate Law: how rate depends on concentration
  • Integrated Rate Law: how concentration depends on time
• How do you determine the rate law from experimental data?

  Analyze the initial rates and concentrations
• What is the overall reaction order?

  Sum of the order of each component in the rate law
• What is the integrated first-order rate law equation?

  ln[A] = -kt + ln[A]₀
• What indicates a first-order reaction on a graph?

  A straight line when plotting ln[A] versus time
• What indicates a second-order reaction on a graph?

  A straight line when plotting 1/[A] versus time
• What is the half-life for a first-order reaction?

  t_1/2 = ln2/k

  • Does not depend on concentration
• What is the half-life equation for a second-order reaction?

  t_1/2 = 1/k[A]₀
• What is the half-life equation for a zero-order reaction?

  t_1/2 = [A]₀/2k
• What is a reaction mechanism?

  A series of steps by which a reaction occurs
• What is an intermediate in a reaction mechanism?

  Formed in one step and used in another
• What is molecularity?

  Number of species colliding to produce a reaction
• What is the rate-determining step (RDS)?

  The slowest elementary step in a reaction
• How does the collision model explain reaction rates?

  Molecules must collide to react, but not all collisions lead to reactions
• What is the Arrhenius equation used for?

  To show how rate depends on temperature and activation energy
• What effect does temperature have on reaction rates?

  Higher temperature increases the reaction rate
• What is a catalyst?

  A substance that speeds up a reaction without being consumed
• What is the difference between homogeneous and heterogeneous catalysts?

  Homogeneous catalysts are in the same phase; heterogeneous are in different phases
• How do catalysts work?

  • Allow reactions to proceed by a different mechanism
  • Provide a new pathway with lower activation energy
  • Do not change the enthalpy of the reaction
• What happens to the rate of reaction when more reactants are added beyond a certain point?

  The rate will not change and becomes zero order