Rate Equations

• What does the rate equation relate mathematically?

  The rate of reaction to reactant concentration
• What is the generalised rate equation for the reaction aA + bB → products?

  r = k[A]m[B]n
• What does the symbol r represent in the rate equation?

  Rate of reaction
• What is the unit of r in the rate equation?

  mol dm^-3 s^-1
• What do the square brackets [A] signify in the rate equation?

  The concentration of reactant A
• What is k in the rate equation?

  The rate constant
• What are m and n in the rate equation?

  Reaction orders
• What does a reaction order of 0 indicate?

  No effect of concentration on reaction rate
• What does a reaction order of 1 indicate?

  Rate is directly proportional to concentration
• What does a reaction order of 2 indicate?

  Rate is proportional to concentration squared
• How are reaction orders determined?

  Experimentally, not from stoichiometric coefficients
• How is the total order of a reaction calculated?

  By adding individual orders m and n
• What is the unit of k for a first-order reaction?

  s^-1
• What is the unit of k for a second-order reaction?

  mol^-1dm³s^-1
• What is the unit of k for a third-order reaction?

  mol^-2dm⁶s^-1
• What happens to the value of k when temperature increases?

  It increases
• What is a continuous rate method?

  Monitoring change in concentration over time
• What does the gradient of a concentration vs. time graph represent?

  The rate of reaction
• What does a horizontal line on a concentration vs. time graph indicate?

  The reaction has stopped
• What is a common method for measuring gas volume in reactions?

  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 graph?

  From the gradient at time = zero
• What is pseudo-zero order in reactions?

  When a reactant's concentration is in excess
• How does the concentration of reactants affect the rate?

  Higher concentration increases the rate
• What is the relationship between the amount of product and moles of reactant?

  Amount of product is proportional to moles of reactant
• What is a clock reaction?

  A reaction with a sudden color change
• How can the order of reaction be determined in clock reactions?

  By varying the concentration of one reactant
• What does the initial rate of a reaction represent in clock reactions?

  It can be represented as (1/t)
• How do you deduce the rate equation from experimental data?

  By comparing experiments with varying concentrations
• What is the overall rate equation for the reaction A + B + 2C → D + 2E?

  r = k[A][B]²
• How is the order of a reactant determined from experiments?

  By comparing rates when concentrations change
• What does a graph of log rate vs log [Y] represent?

  A straight line where the gradient equals order n
• What is the significance of the y-intercept in a log rate graph?

  It represents log K
• What happens when two reactant concentrations are changed simultaneously?

  The overall change on rate is multiplied
• How do you calculate the order when both reactants are changed?

  By multiplying the effects of individual changes
• What is the equation for log rate?

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

  A straight line with gradient n
• What is the rate equation format mentioned?

  Y = c + m x
• What causes 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 one at a time
  • Measure the initial rate each time