How Fast

• What is the definition of the rate of reaction?

  Change in concentration per unit time
• How can you calculate the rate of reaction at a given instant?

  Rate = change in concentration / time
• What does it mean if the order is zero with respect to a reactant?

  Concentration change has no effect on rate

  
• What is the effect on rate in a first order reaction?

  Rate is directly proportional to concentration
• What is the effect on rate in a second order reaction?

  Change in rate = change in concentration squared
• What is the generic rate equation and what do its terms mean?

  • Rate = k [X]^x [Y]^y
  • k = rate constant
  • [X] and [Y] = concentrations of species
  • x and y = orders of reaction
• Do zero order reactants appear in the rate equation? Why?

  No, they don't affect the rate

  
• How is the overall order of a reaction calculated?

  Sum of individual orders
• How would you calculate the units of the rate constant?

  Use units of rate and concentration
• What are the units of rate?

  mol dm-3 s-1
• What are the units of concentration?

  mol dm-3
• What are the units for the rate constant when the overall order is 3?

  dm6 mol-2 s-1
• How could you measure the rate of reaction experimentally?

  Use a colorimeter or gas syringe
• What does half-life mean?

  Time for concentration to decrease by half
• What is the symbol for half-life?

  t 1/2
• How do concentration-time graphs differ for zero and first order reactants?

  • Zero order: linear decrease
  • First order: exponential decrease

  
• What is the relationship between first order reactions and half-life?

  First order reactants have constant half-lives
• What is the equation for rate constant using half-life in a first order reaction?

  k = ln2 / t 1/2
• How would you draw a rate concentration graph?

  Plot [A] against time, then rate

  
• What is the relationship between rate and time?

  Rate ∝ 1/t
• How do rate concentration graphs differ for zero, first, and second order reactants?

  • Zero order: linear graph
  • First order: curve graph
  • Second order: steep curve graph

  
• How to determine the rate constant from a rate concentration graph of first order?

  k = rate / concentration
• What is the rate determining step?

  Slowest step in a multi-step reaction
• How does the rate determining step link to the species in the rate equation?

  Species in rate step appear in rate equation
• What indicates how many molecules of a reactant are involved in the rate determining step?

  The order of the reactant
• In the rate equation rate = k[NO]2 , how many molecules of NO are in the rate determining step?

  2
• What affects the value of the rate constant for a given reaction?

  Temperature, nothing else
• What is the effect of a 10℃ temperature increase on the rate of reaction?

  Doubles the rate of reaction
• What is the Arrhenius equation and what do its terms mean?

  • Arrhenius equation: k = Ae-Ea/RT
  • k = rate constant
  • A = pre-exponential factor
  • Ea = activation energy
  • R = gas constant
  • T = temperature in Kelvin

  
• How can you convert the Arrhenius equation into a useful form for plotting a graph?

  ln k = -Ea/RT + ln A
• What does the gradient of the graph of ln k against 1/T represent?

  Gradient = -Ea/R
• What does the y-intercept of the graph of ln k against 1/T represent?

  1. intercept = ln A