equilibria & rate equations

• What does the reaction rate measure?

  The change in concentration of reactant or product per unit time
• What are the units of reaction rate?

  mol/dm³/s
• What is the rate equation defined by?

  The concentration of reactants
• What does k represent in the rate equation?

  K is the rate constant
• How does temperature affect the rate constant?

  The rate constant changes with temperature
• What are A and B in the rate equation?

  A and B are the concentrations of reactants
• What is the effect of a catalyst on the rate equation?

  A catalyst is included in the rate equation even if it is not part of the chemical reaction
• What do m and n represent in the rate equation?

  m and n are the orders of reaction
• What does the order of a reactant indicate?

  It shows how the reactant concentration affects the rate of reaction
• What effect does the first order have mean for the equilibrium concentration?

  It is directly proportional to the concentration of that reactant
• How does the second order of reaction relate to reactant concentration?

  It is proportional to the square of the reactant concentration
• How is the overall order of reaction determined?

  It is the sum of the powers of the reactants in the rate equation
• How must the rate equation be determined?

  It must be done from experimental data
• What is the process for determining the rate equation from experimental data?

  • Conduct experiments to measure the rate of reaction
  • Analyze how changes in reactant concentrations affect the rate
  • Use the data to derive the rate equation
• In the example reaction rate = [A][B]^2, what happens when the concentration of B is doubled?

  The rate increases by a factor of 4
• What does the Arrhenius equation show?

  It shows how temperature affects the rate constant
• What is the Arrhenius equation?

  $k =$$A e^{-\frac{E_a}{RT}}$
• What does $E_a$ represent in the Arrhenius equation?


  Activation energy in J/mol
• What is the value of the gas constant $R$?


  $8.314 \text{ J/(mol K)}$
• What governs the rate of the whole reaction process?

  The rate of the slowest step in a reaction
• What will appear in the rate equation regarding the rate-determining step?

  The concentrations of reactants up to and including the rate-determining step
• In the example A + B → products, if step 1 is the rate-determining step, what is the rate equation?

  Rate = k[A][B]
• What is the purpose of measuring gas volume using a gas syringe?

  To plot a graph of volume vs. time to determine the initial rate of reaction
• How can the initial rate of reaction be determined from a mass loss graph?

  By plotting mass loss vs. time and finding the tangent at time zero
• Why is cotton wool used in the neck of a beaker during a reaction with acid?

  To prevent acid from splashing out
• What is a limitation of measuring colored reactants/products?

  It requires a calibration graph and takes a lot of time and effort
• What are the experimental methods for measuring reaction rates?

  • Measuring gas volume using a gas syringe
  • Measuring mass loss over time
  • Monitoring changes in colored reactants/products
• What is dynamic equilibrium?


  It is when forwards and backwards reactions have equal rates.
• What happens to the concentration of reactants and products at dynamic equilibrium?


  The concentrations of reactants and products remain constant.
• What is the equilibrium constant symbol for a system in dynamic equilibrium?

  Kc
• What is ignored in the equilibrium expression?

  Solids are ignored.
• What influences the equilibrium constant?

  The equilibrium constant is only influenced by temperature.
• How does temperature affect the rates of forwards and backwards reactions?

  Temperature affects the rates by different amounts.
• What happens to the equilibrium constant in an exothermic reaction when temperature increases? (assuming forwards is exo)

  The equilibrium constant decreases.
• How can the equilibrium expression for gaseous reactions be written?

  It can be written in terms of partial pressures.
• What is the general form of the equilibrium expression for a reaction aA + bB ⇌ cC + dD?

  The expression is Kp = (pC)^c x (pD)^d /(pA)^a x (pB)^b
• What is the unit of partial pressure?

  It can be measured in kPa or Pa.
• How does a change in concentration affect the position of equilibrium?

  A change in concentration affects the position of equilibrium and the Kp value.
• What is the definition of partial pressure?

  It is the pressure a gas would exert in a container on its own.
• What does Dalton's Law state about total pressure?

  Total pressure is the sum of partial pressures.