kinetics 2

• What does the rate of a reaction indicate?

  It shows how fast reactants are converted into products.
• What factors does the rate of reaction depend on?

  It depends on the concentrations of the reactants and the rate constant.
• What is the rate equation for the reaction A + B → C?


  Rate = k[A]​m​[B]​n
• What do the constants m and n in the rate equation represent?

  They show the order of the reaction with respect to that species.
• What values can m and n take in a rate equation?

  They can be 0, 1, or 2.

  
• How is the total order of reaction calculated?

  Total order = m + n
• When is the rate constant (k) considered constant?

  When the reaction temperature is constant.
• What does the rate constant relate to in a reaction?

  It relates the concentrations of the species that affect the rate of a reaction to the overall rate of reaction.
• How can the rate constant k be calculated?

  By rearranging the rate equation for that reaction.
• What affects the units of the rate constant k?

  They vary depending on the number of species and their orders of reaction.
• What is the order of reaction that students need to know at A-Level?

  From zero to second order.
• What are the characteristics of zero order reactions?

  • Concentration has no impact on rate.
  • Shown as a horizontal line on a rate-concentration graph.
  • Rate = k

  
• What are the characteristics of first order reactions?

  • Concentration and rate are directly proportional.
  • Doubling the concentration doubles the rate.
  • Rate = k[A]

  
• What are the characteristics of second order reactions?

  • Rate is proportional to the concentration squared.
  • Doubling the concentration increases the rate by four times.
  • Rate = k[A]​2

  
• How can reaction orders be determined from concentration-time graphs?

  By analyzing the shapes of the graphs generated during the experiment.
• What shape does a concentration-time graph for a zero order reaction have?

  It is linear.
• What shape do concentration-time graphs for first and second order reactions have?

  They are curved.
• How can the initial rate of a reaction be determined?

  By varying the concentrations of reactants and measuring the initial rate of the reaction.
• What are the effects of doubling the concentrations of reactants on the initial rate for different orders?

  • Zero order: No change to the initial rate.
  • First order: Initial rate doubles.
  • Second order: Initial rate quadruples (2²).

  
• What is the definition of half-life (t​1/2​)?

  It is the time taken for the initial concentration of the reactants to decrease by half.
• How does the half-life of a first order reaction behave throughout the reaction?

  It is constant throughout the reaction.
• What are the two general ways to investigate reaction rates experimentally?

  1. Measuring the change in a reactant mass or concentration over time.
  2. Measuring the change in a product mass or concentration over time.

  
• How can raw data from reactions be used?

  It allows for the generation of concentration-time graphs, mass-time graphs, or volume-time graphs to calculate the rate of reaction.
• What happens to the mass of the reaction mixture if a gas is produced?

  The mass will decrease as the reaction proceeds.
• How can the rate of reaction be found if a gas is produced?

  By measuring the volume of gas produced over the course of the reaction.
• What equipment can be used to collect gas produced in a reaction?

  A gas syringe or an underwater upside-down measuring cylinder.
• What is the purpose of titration in reaction rate experiments?

  • Small samples of a reaction mixture are removed at regular intervals.
  • These samples are titrated to determine the concentration of a given reactant or product.
  • A concentration-time graph can then be plotted.

  
• How does colorimetry determine the rate of reaction?

  • It measures the amount of light absorbed by a solution.
  • The amount of light absorbed is proportional to the concentration of the colored species.
  • A calibration curve is generated to convert absorbance readings into concentration values.

  
• What color change occurs in the iodination of propanone as iodine is used up?

  The color changes from brown to orange, to yellow, and finally to colorless.
• What determines the overall rate of a reaction?

  The overall rate is determined by the slowest step of the reaction, known as the rate determining step.
• How can the rate determining step be identified from a reaction sequence?

  By looking at which steps include the species in the rate equation.
• What does the rate equation indicate about the rate determining step?

  • The powers in the rate equation indicate the number of molecules of each substance involved in the slowest step.
  • Any intermediates generated in the slowest step must be reactants in another step.

  
• What is the rate equation for the reaction of nitrogen dioxide and carbon monoxide?

  rate = k[NO​2​]​2
• What does the reaction mechanism for S​N​1 reactions include?

  The rate equation includes the concentration of the halogenoalkane only.
• What does the reaction mechanism for S​N​2 reactions include?

  The rate equation includes both the concentration of the halogenoalkane and the concentration of the nucleophile.
• What factors affect the rate of S​N​1 reactions?

  The rate depends on the stability of the carbocation intermediate.
• What factors affect the rate of S​N​2 reactions?

  The rate depends on how easily the nucleophile can access the carbon attached to the leaving group.
• What are the key differences between S​N​1 and S​N​2 reactions?

  • S​N​1: Two steps, rate determined by carbocation stability, rate equation includes halogenoalkane only.
  • S​N​2: One step, rate determined by nucleophile access, rate equation includes both halogenoalkane and nucleophile.
• How does the Arrhenius equation relate the rate constant k and temperature?

  It shows how k and temperature are related exponentially.
• What is the logged form of the Arrhenius equation used for?

  It can be used to show the relationship graphically in the form ‘y = mx + c’.