Kinetics

• What does the rate equation relate mathematically?

  The rate of reaction to the concentration of the reactants
• 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 A in mol dm^-3
• What is k in the rate equation?

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

  Reaction orders
• What do the reaction orders (m, n) indicate?

  The effect of the concentration of reactants on the rate of reaction

  
• How are reaction orders determined?

  Experimentally, not from the balanced equation
• What is the total order of a reaction?

  The sum of all individual orders (m+n)
• What does a zero order mean for a reactant's concentration?

  The concentration has no effect on the rate of reaction
• What does first order mean in terms of concentration?

  The rate of reaction is directly proportional to the concentration of A
• What does second order mean in terms of concentration?

  The rate of reaction is proportional to the concentration of A squared

  
• How does the unit of k change with the overall order of reaction?

  The units of k depend on the overall order of reaction
• What happens to the value of k when temperature increases?

  The value of k increases
• What is the unit of k for a first order overall reaction?

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

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

  mol^-2dm⁶s^-1
• What is the process of calculating the units of k?

  1. Rearrange the rate equation to isolate k: k = Rate / [A]^m[B]^n
  2. Insert units and cancel:

  • k = mol dm^-3s^-1 / (mol dm^-3)^m(mol dm^-3)ⁿ

  1. Simplify to find the unit of k.
• What is a continuous rate method?

  A method that records the change in concentration over time
• What does the gradient of a concentration vs. time graph represent?

  The rate of reaction

  
• When is the reaction fastest in a continuous monitoring method?

  At the start, where the gradient is steepest
• What happens to the gradient as reactants are used up in a reaction?

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

  Using a gas syringe
• What should be considered when using a gas syringe for measuring gas volume?

  The reaction should not produce more than the syringe's capacity
• How is the initial rate calculated in a continuous monitoring method?

  From the gradient of the concentration vs. time graph at time = zero
• What is a pseudo-zero order reactant?

  A reactant in large excess that appears not to affect the rate
• How does the concentration of reactants affect the rate of reaction?

  Higher concentration increases the rate
• What is the initial rate method?

  A method to calculate the initial rate from the gradient of a concentration vs. time graph
• What indicates the end point in a clock reaction?

  A sudden color change when a limited reactant runs out
• What is a common clock reaction example?

  Hydrogen peroxide reacting with iodide ions to form iodine
• How can the order of reaction be determined in clock reactions?

  By varying the concentration of a reactant and measuring the time taken for a color change
• What is the relationship between initial rate and concentration in experiments?

  The initial rate can be represented as (1/t) where t is the time taken for a color change
• How do you deduce the rate equation from experimental data?

  By comparing experiments where only one reactant's concentration is changed
• What is the overall rate equation for the reaction A + B + 2C → D + 2E based on the provided data?

  r = k[A][B]^2
• How do you determine the order of a reactant when comparing two experiments?

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

  
• What happens to the rate when the concentration of reactant A is doubled while keeping B and C constant?

  If the rate doubles, A is first order; if it stays the same, A is zero order; if it quadruples, A is second order
• How do you calculate the overall order of a reaction?

  By adding the individual orders of all reactants
• What is the significance of the gradient in a log(rate) vs log([Y]) graph?

  The gradient represents the order n of the reaction

  
• What is the effect of changing two reactant concentrations simultaneously on the rate?

  The overall change in rate is the product of the individual changes in concentration