General Chemistry Exam IV Study Guidance: Kinetics & Electrochemistry

Q1. Which of the following is consistent with the reaction below being third order overall?

2 A + B + C → D + E

Background

Topic: Reaction Order & Rate Laws

This question tests your understanding of how to determine the overall order of a reaction from its rate law and related properties.

Key Terms and Formulas:

• Rate Law: An expression relating the rate of a reaction to the concentrations of reactants.

• Overall Order: The sum of the exponents in the rate law.

• Units of Rate Constant: Depend on the overall order.

Step-by-Step Guidance

1. Recall that the overall order is the sum of the exponents in the rate law. For example, Rate = k[A]^2[B][C] is third order overall (2+1+1).

2. Check the units of the rate constant for a third order reaction. For third order, k has units of M-2s-1.

3. Eliminate options that do not match the definition or units for a third order reaction.

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Q2. What is the rate law expression for the reaction below, given the following data:

HgCl2(aq) + C2O42–(aq) → 2 Cl–(aq) + 2 CO2(g) + Hg2Cl2(s)

Background

Topic: Determining Rate Laws from Experimental Data

This question tests your ability to analyze experimental data to deduce the rate law for a reaction.

Key Terms and Formulas:

• Rate Law: Rate = k[HgCl2]^x[C2O42–]^y

• Initial Rate Method: Compare changes in concentration and rate to determine exponents.

Step-by-Step Guidance

1. Compare trials where only one reactant concentration changes to determine the order with respect to each reactant.

2. Calculate the ratio of rates and concentrations to solve for the exponents x and y.

3. Write the rate law using the determined exponents.

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Q3. A reaction A + B → products has the following rate law: Rate = k [A]^m [B]^1

At a certain temperature, the rate is 4.78 × 10–2 Ms–1 when [A] = 1.12 M and [B] = 0.87 M. The rate constant is 4.38 × 10–2 M–2s–1. What is the order with respect to A?

Background

Topic: Rate Law and Reaction Order

This question tests your ability to use the rate law and given data to determine the reaction order with respect to a specific reactant.

Key Terms and Formulas:

• Rate Law: Rate = k[A]^m[B]^1

• Order with respect to A: The exponent m in the rate law.

Step-by-Step Guidance

1. Write the rate law with the given values: $\text{Rate} = k[A]^m[B]^1$.

2. Plug in the values for Rate, k, [A], and [B].

3. Rearrange the equation to solve for m using logarithms if necessary.

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Q18. Consider E°red(Fe3+/Fe2+) = +0.77 V and the following diagram of a standard galvanic cell:

Background

Topic: Electrochemistry – Galvanic Cells

This question tests your understanding of standard cell notation, electrode processes, and the interpretation of cell diagrams.

Key Terms and Formulas:

• Galvanic Cell: A device that generates electrical energy from spontaneous redox reactions.

• Cathode: Electrode where reduction occurs.

• Anode: Electrode where oxidation occurs.

• Standard Reduction Potential ($E^\circ_{\text{red}}$): The voltage associated with a reduction half-reaction at standard conditions.

Step-by-Step Guidance

1. Identify which electrode is the cathode and which is the anode based on the cell diagram and reduction potentials.

2. Recall that reduction occurs at the cathode and oxidation at the anode.

3. Determine which species are being oxidized and reduced in the cell.

4. Analyze the voltmeter reading and relate it to the standard reduction potential.

5. Check the material of the electrodes and the direction of electron flow.

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