Pmt flashcards chapter 18

• What is the definition of 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 a 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 do you calculate the units of the rate constant?

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

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

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

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

  • Use a colorimeter for color change
  • Use a gas syringe for gas volume
  • Measure change in mass of mixture
• What does half-life mean?

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

  t_1/2
• How does a concentration-time graph look for a zero order reactant?

  • Linear decrease
  • Slope represents rate

  
• How does a concentration-time graph look for a first order reactant?

  • Exponential decrease
  • Rate decreases over time

  
• 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 do you draw a rate concentration graph?

  • Plot [A] against time
  • Draw tangents at different values
  • Draw secondary graph of rate against [A]

  
• What is the relationship between rate and time?

  Rate ∝ 1/t
• How does a rate concentration graph look for a zero order reactant?

  • Horizontal line
  • Rate is constant

  
• How does a rate concentration graph look for a first order reactant?

  • Curved line
  • Rate decreases as concentration decreases

  
• How does a rate concentration graph look for a second order reactant?

  • Steep curve
  • Rate increases with concentration squared

  
• 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 equation?

  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?

  • k = A e^-Ea/RT
  • k = rate constant
  • A = frequency 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/R * (1/T) + ln A
  • Graph of ln k against 1/T is straight line
  • Gradient = -Ea/R, y-intercept = ln A