Q1. For the reaction N2 + 3 H2 → 2 NH3, the average rate of consumption of H2 is 0.0277 M/s. What is the average rate of change (M/s) for production of NH3?

Background

Topic: Reaction Rates and Stoichiometry

This question tests your understanding of how reaction rates relate to the stoichiometry of a balanced chemical equation. You need to connect the rate of consumption of one reactant to the rate of formation of a product using their stoichiometric coefficients.

Key Terms and Formulas

• Average rate: Change in concentration of a reactant or product per unit time.

• Stoichiometry: The quantitative relationship between reactants and products in a balanced equation.

General rate expression for aA + bB → cC + dD:

Step-by-Step Guidance

1. Write the balanced equation:

2. Identify the given rate: The rate of consumption of is .

3. Set up the rate relationship using stoichiometry:

   • For :

   • For :

4. Relate the rates using the coefficients:

Try solving on your own before revealing the answer!

Q2. The reaction 2 H2 + 2 NO2 → N2 + 2 H2O has the rate law: rate = k[H2]2[NO]. What is the rate of the reaction (M/s) if the rate constant k is 6.0 x 104 (M-2/s) with [H2] = 0.0010 M and [NO] = 0.0020 M?

Background

Topic: Rate Laws and Calculating Reaction Rates

This question tests your ability to use a given rate law to calculate the reaction rate when provided with the rate constant and reactant concentrations.

Key Terms and Formulas

• Rate law: An equation that relates the reaction rate to the concentrations of reactants and the rate constant.

• Rate constant (k): A proportionality constant specific to a reaction at a given temperature.

Given rate law:

Step-by-Step Guidance

1. Write the rate law:

2. Identify the given values:

3. Substitute the values into the rate law:

4. Calculate and multiply by (but do not finish the calculation yet).

Try solving on your own before revealing the answer!

Q3. Determining the rate law from kinetic data

Background

Topic: Experimental Determination of Rate Laws

This question tests your ability to analyze experimental data to determine the order of reaction with respect to each reactant and write the rate law.

Key Terms and Formulas

• Order of reaction: The exponent to which the concentration of a reactant is raised in the rate law.

• Initial rate method: Comparing how the initial rate changes as concentrations are varied.

General rate law:

Step-by-Step Guidance

1. Compare experiments where only one reactant concentration changes to determine the order with respect to that reactant.

2. For [NO]: Compare experiments 1 and 2 (where [H2] is constant).

3. For [H2]: Compare experiments 1 and 3 (where [NO] is constant).

4. Use the ratio method:

   • For example, (if [H2] is constant)

5. Solve for the exponents m and n (but do not write the final rate law yet).

Try solving on your own before revealing the answer!

Q4. What is the half-life of a first order reaction?

Background

Topic: Kinetics – First Order Reactions

This question tests your understanding of the half-life formula for first order reactions and how it relates to the rate constant.

Key Terms and Formulas

• Half-life (): The time required for the concentration of a reactant to decrease by half.

• First order reaction: A reaction whose rate depends linearly on the concentration of one reactant.

Half-life formula for first order reactions:

Step-by-Step Guidance

1. Identify that the reaction is first order.

2. Recall the half-life formula:

3. Recognize that you need the value of the rate constant to calculate the half-life.

Try solving on your own before revealing the answer!

Q5. The activation energy of a reaction is 56.8 kJ/mol and the frequency factor is 1.5 x 1011/s. Calculate the rate constant of the reaction at 25°C using the one-point Arrhenius equation.

Background

Topic: Arrhenius Equation – Temperature Dependence of Rate Constants

This question tests your ability to use the Arrhenius equation to calculate the rate constant at a given temperature, given the activation energy and frequency factor.

Key Terms and Formulas

• Arrhenius equation:

• Activation energy (): The minimum energy required for a reaction to occur (in J/mol).

• Frequency factor (): The pre-exponential factor related to the frequency of collisions.

• R: Gas constant,

• T: Temperature in Kelvin

Step-by-Step Guidance

1. Convert the activation energy from kJ/mol to J/mol:

2. Convert the temperature to Kelvin:

3. Write the Arrhenius equation:

4. Substitute the values for , , , and into the equation (but do not calculate the exponent yet).

Try solving on your own before revealing the answer!

Q6. A reaction has a rate constant k of 3.20 x 10-5/s at 450 K and a rate constant k of 9.40 x 10-3/s at 500 K. What is the activation energy Ea for this reaction?

Background

Topic: Arrhenius Equation – Two-Point Form

This question tests your ability to use the two-point Arrhenius equation to determine the activation energy from rate constants at two different temperatures.

Key Terms and Formulas

• Arrhenius equation (two-point form):

• , : Rate constants at temperatures and

Step-by-Step Guidance

1. Write the two-point Arrhenius equation:

2. Identify the given values:

   • at

   • at

3. Calculate (but do not compute the value yet).

4. Calculate (but do not compute the value yet).

5. Set up the equation to solve for (but do not isolate $E_a$ yet).

Try solving on your own before revealing the answer!