5.1 Rates, Orders & Arrhenius

• How can the rate of reaction be found?

  By measuring concentration change over time

  
• What are the units for the rate of reaction?

  mol dm$^{-3} s^{-1}$
• What is the general reaction used to study the rate of reaction?

  D (aq) → E (aq) + F (g)
• What relationship is observed between the rate of reaction and concentration of D?

  A directly proportional relationship

  
• What does the rate expression Rate = k[D] indicate?

  Doubling concentration of D doubles the rate
• What is the rate equation for the reaction A (aq) + B (aq) → C (aq) + D (g)?

  Rate = k[A][B]
• How are rate equations determined?

  Experimentally, not from stoichiometric equations
• What do [A] and [B] represent in the rate equation?

  The concentrations of the reactants

  
• What does the order of a reactant indicate?

  How concentration affects the rate of reaction

  
• What values can the order of a reaction take?

  Positive, negative, or fractional values
• What does an order of 0 indicate about a reactant?

  No effect on the rate of reaction
• What does an order of 1 indicate about a reactant?

  Concentration is directly proportional to rate

  
• What does an order of 2 indicate about a reactant?

  Rate is proportional to the square of concentration

  
• How is the overall order of reaction calculated?

  Sum of the powers of the reactants
• How do you determine the order with respect to each reactant?

  By analyzing experimental data from reactions
• How can the rate constant (k) be calculated?

  Using initial rates and the rate equation

  
• What is the method to deduce the units for the rate constant (k)?

  By substituting values in the rate equation

  
• What does a zero-order reaction indicate about the concentration-time graph?

  Concentration decreases inversely with time

  
• What does the gradient of a zero-order reaction graph represent?

  The rate of reaction

  
• What characterizes a first-order reaction graph?

  Concentration decreases and eventually plateaus

  
• How does a second-order reaction graph differ from a first-order graph?

  It decreases more steeply with time

  
• How can the order of a reaction be deduced from its half-life?

  By observing changes in half-life over time
• What happens to the half-lives of a zero-order reaction?

  Successive half-lives decrease with time

  
• What is true about the half-life of a first-order reaction?

  It remains constant throughout the reaction
• What happens to the half-life of a second-order reaction?

  It increases with time
• What is the general form of a rate equation?

  Rate = k[reactants]
• What is the significance of the rate constant (k)?

  It indicates the speed of the reaction

  
• What are the characteristics of zero, first, and second-order reactions regarding concentration-time graphs?

  • Zero-order: Straight line down, concentration inversely proportional to time
  • First-order: Curve downwards, concentration decreases and plateaus
  • Second-order: Steeper curve downwards, concentration decreases more steeply

  
• How do half-lives differ among zero, first, and second-order reactions?

  • Zero-order: Successive half-lives decrease
  • First-order: Half-life remains constant
  • Second-order: Half-life increases with time

  
• What is the process for deriving rate equations from experimental data?

  1. Identify experiments where one reactant changes, others constant
  2. Determine order for each reactant individually
  3. Combine orders to form the rate equation
• What type of graph is used to represent a second-order reaction?

  Concentration-time graph

  
• How can the order of a reaction be deduced?

  From its half-life
• What happens to half-lives in a zero-order reaction?

  Successive half-lives decrease with time

  
• How does the half-life of a first-order reaction behave?

  It remains constant throughout the reaction
• What is the behavior of half-lives in a second-order reaction?

  Half-life increases with time
• What are the half-lives of zero, first, and second-order reactions?

  • Zero-order: decreases with time
  • First-order: constant throughout
  • Second-order: increases with time

  
• In a zero-order reaction, how does the rate depend on the concentration of the reactant?

  The rate remains constant

  
• What does the graph of a zero-order reaction look like?

  It is a horizontal line

  
• What is the rate equation for a zero-order reaction?

  rate = k

  
• How does the rate of a first-order reaction change with concentration?

  It is directly proportional to concentration