Rates

• How is the rate of reaction defined?

  Change in concentration over time
• The units of reaction rate are moldm$^{ - 3}$ s$^{ - 1}$
• What is activation energy, Eᴀ?

  Minimum energy to start reaction
• When the concentration of a reactant increases, the rate of reaction increases
• Increasing temperature increases the number of particles with energy greater than Eᴀ.
• How do catalysts affect the activation energy of a reaction?

  Lower it
• A rate equation shows the relationship between the rate of a reaction and the initial concentrations
• How is the overall order of a reaction calculated?

  Sum of orders
• What is the rate constant, k, in a rate equation?

  Proportionality constant
• For a first-order reaction, the units of k are s$^{ - 1}$
• Steps in the initial rates method for determining the rate equation

  1️⃣ Carry out experiments with different initial concentrations

  2️⃣ Change one variable at a time (A or B)

  3️⃣ Determine the order with respect to each reactant

  4️⃣ Write the rate equation

  5️⃣ Calculate the value and units of k
• Match the experimental data with the rate equation:

  Rate doubles when [H$^ +$] doubles ↔️ First order with respect to H$^ +$

  Rate quadruples when [J] doubles ↔️ Second order with respect to J

  Rate is unaffected by changes in [H$^ +$] ↔️ Zero order with respect to H$^ +$
• The shape of a rate-concentration graph can be used to deduce the order of the reaction with respect to the reactant.
• What does a straight-line graph through the origin on a rate-concentration graph indicate?

  First-order kinetics
• In a concentration-time graph, the rate decreases as the concentration of the reactant decreases for a first-order reaction.
• The gradient of a concentration-time graph at a particular time is a measure of the rate at that time.
• What does the gradient of a concentration-time graph measure?

  Reaction rate
• The gradient of a concentration-time graph at a particular time is a measure of the reaction rate at that time.
• Steps in a continuous monitoring method for measuring reaction rate

  1️⃣ Start with known concentrations of reactants A and B

  2️⃣ Ensure concentration of only one reactant (A) changes significantly

  3️⃣ Determine the concentration of A at different times

  4️⃣ Measure changes in volume, pH, mass, or absorbance
• Quenching a reaction involves placing the reaction mixture in an ice bath to stop it.
• What type of graph is plotted to analyze reaction rates?

  Concentration vs. time
• The rate determining step is the slowest step in a reaction mechanism
• Any step after the rate determining step affects the overall reaction rate.

  False
• What is the rate equation for the reaction A + B → C + D?

  Rate = k[A][B]
• Steps in the reaction mechanism for X + 2Y → Z

  1️⃣ 2Y → A

  2️⃣ A + X → Z
• The order of each reactant is the molar ratio in the rate determining step.
• The rate of reaction always increases when the temperature is increased.
• Match the term with its definition in the Arrhenius equation:

  k ↔️ Rate constant

  A ↔️ Arrhenius constant

  Eᴀ ↔️ Activation energy

  T ↔️ Temperature in Kelvin
• The units of activation energy (Eᴀ) are kJ mol$^{ - 1}$, while the units of the gas constant (R) are J K$^{ - 1}$ mol$^{ - 1}$.J
• How does the rate constant, k, change with increasing temperature according to the Arrhenius equation?

  Exponentially increases
• The relationship between the rate constant and temperature is described by the Arrhenius equation.
• Match each variable in the Arrhenius equation with its correct description:

  k ↔️ Rate constant

  A ↔️ Arrhenius constant

  E_a ↔️ Activation energy

  R ↔️ Gas constant

  T ↔️ Temperature in Kelvin
• The units of activation energy, E_a, are kJ mol$^{ - 1}$, and the units of R are J K$^{ - 1}$ mol$^{ - 1}$.
• To convert the units of E_a from kJ mol$^{ - 1}$ to J mol$^{ - 1}$, multiply by 10$^{3}$.
• What is the natural log form of the Arrhenius equation?

  $\ln k =$$\ln A - \frac{E_{a}}{RT}$
• The natural log form of the Arrhenius equation can be used to calculate activation energy.
• A graph of ln k against 1/T produces a straight line with a negative gradient.
• The gradient of the ln k vs 1/T graph is equal to -E_a/R.
• How is the activation energy, E_a, calculated from the gradient of the ln k vs 1/T graph?

  E_a = -gradient x R