Rate equations

• What does the rate equation relate mathematically?

  The rate of reaction to the concentration of the reactants
• What does a reaction order of 0 indicate about a reactant's concentration?

  The concentration has no effect on the rate of reaction

  
• How is the total order of a reaction calculated?

  By adding all the individual orders together (m+n)
• What does a first order reaction imply about the rate of reaction?

  The rate is directly proportional to the concentration of the reactant

  
• What is the rate equation for a second order reaction with respect to A?

  r = k[A]^2
• How does the value of \( k \) change with temperature?

  It increases if the temperature increases
• What is the unit of \( k \) for a first order overall reaction?

  s^-1
• What is the process of continuous monitoring in rate equations?

  • Following one experiment over time
  • Recording the change in concentration
  • The gradient represents the rate of reaction
  • The reaction rate is fastest at the start
• What does the gradient of a concentration vs. time graph represent?

  The rate of reaction

  
• What happens to the rate of reaction as reactants are used up?

  The rate drops as their concentration decreases
• What is a common method for measuring gas volume in a reaction?

  Using a gas syringe
• What is the initial rate of a reaction?

  The rate at the start of the reaction
• How can the initial rate be calculated from a continuous monitoring graph?

  From the gradient at time = zero
• What does it mean for a reactant to be in large excess?

  It appears not to affect the rate and is pseudo-zero order
• What factors affect the rate of reaction?

  • Concentration of reactants
  • Temperature
  • Surface area
  • Presence of catalysts
• How is the initial rate calculated from clock reactions?

  By measuring the time taken to reach a fixed concentration
• What happens in a clock reaction when the limited reactant runs out?

  A sudden colour change occurs
• How can the order of reaction with respect to a reactant be determined in clock reactions?

  By varying the concentration of that reactant while keeping others constant
• What is the relationship between the initial rate and the time taken in clock reactions?

  The initial rate is represented as \( \frac{1}{t} \)
• How can the order of a reactant be calculated by comparing experiments?

  By observing how the rate changes when the concentration of that reactant is varied

  
• What is the overall rate equation derived from the experiments provided?

  r = k[A][B]^2
• How is the order of a reactant determined when both reactant concentrations are changed simultaneously?

  The effect of both individual changes on concentration are multiplied together

  
• What is the process for working out orders from experimental initial rate data?

  1. Change initial concentrations of reactants one at a time
  2. Measure the initial rate each time
  3. Compare the rates to determine the order

  
• What is the equation for the log rate in relation to concentration?

  Log rate = log k + n log [Y]
• What does a graph of log rate vs log [Y] represent?

  A straight line where the gradient is equal to the order n
• What is the general form of the rate equation mentioned?

  Y = c + m x
• What factors contribute to the biggest percentage errors in experiments?

  High concentrations with quick times
• How do you work out orders from experimental initial rate data?

  • Conduct a series of experiments
  • Change initial concentrations of reactants one at a time
  • Measure the initial rate each time
• What does the y-intercept represent in the log(rate) graph?

  The y-intercept is log K
• How is the gradient of the log(rate) graph calculated?

  Gradient = change in y / change in x
• How do you work out orders when two reactant concentrations are changed simultaneously?

  • Compare two experiments where one reactant's concentration is changed
  • If both reactants are changed, multiply their individual changes to find overall change on rate

  
• If the concentration of [A] is doubled, how does it affect the rate if the rate equation is r = k [A] [B]^2?

  The rate would double
• If the concentration of [B] is tripled, how does it affect the rate in the equation r = k [A] [B]^2?

  The rate would increase by a factor of 9
• How do you calculate the value of k using initial rate data?

  k = r / ([X] [Y]^2)
• What happens to the value of k when the temperature increases?

  It increases
• What does the Arrhenius equation express?

  k = Ae^-EA/RT
• How do you calculate the Arrhenius constant A using the Arrhenius equation?

  A = k e^EA/RT
• How do you calculate the activation energy using the Arrhenius equation?

  EA = (ln A - ln k) x RT
• What is the relationship between k and the rate of reaction?

  • k is proportional to the rate of reaction
  • ln k can be replaced by ln(rate)
• How can the activation energy be calculated from a graph of ln(rate) against 1/T?

  EA = - gradient x R