Chemical Kinetics: Reaction Rates - Chem 1780-1

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Questions and Answers

What is the average rate of change of [D] over the first 30 minutes?

  • +0.020 M/min (correct)
  • -0.010 M/min
  • -0.020 M/min
  • +0.010 M/min

Which of the following statements about the rate of change is correct?

  • The rate of change is always negative for products.
  • The rate of change is always positive for reactants.
  • The rate of change is always positive for products.
  • The rate of change is always negative for reactants. (correct)

What is the relationship between the rate of consumption of Ag+(aq) and the rate of formation of [Ag(CN)2]−(aq)?

  • The rate of consumption of Ag+(aq) is twice the rate of formation of [Ag(CN)2]−(aq).
  • The rate of consumption of Ag+(aq) is half the rate of formation of [Ag(CN)2]−(aq).
  • The rate of consumption of Ag+(aq) is equal to the rate of formation of [Ag(CN)2]−(aq). (correct)
  • The rate of consumption of Ag+(aq) is four times the rate of formation of [Ag(CN)2]−(aq).

Which of the following is the correct expression for the instantaneous rate of change of D?

<p>d[D]/dt (A)</p> Signup and view all the answers

What is the relationship between the initial rates of A and D?

<p>The initial rate of A is less than the initial rate of D. (B)</p> Signup and view all the answers

How does the rate of loss of CN−(aq) relate to the rate of loss of Ag+(aq)?

<p>The rate of loss of CN−(aq) is twice the rate of loss of Ag+(aq). (A)</p> Signup and view all the answers

Why is it important to properly balance a chemical equation when determining relative rates?

<p>Balancing ensures the correct stoichiometric coefficients, which determine the relationship between the rates of consumption and formation of reactants and products. (B)</p> Signup and view all the answers

What is the difference between average rate and instantaneous rate?

<p>The average rate is calculated over a specific time interval, while the instantaneous rate is the rate at a particular moment in time. (D)</p> Signup and view all the answers

Flashcards

Chemical Kinetics

The study of reaction rates and how they change.

Rate of Change

The speed at which a concentration of reactants or products changes over time.

Average Rate

The change in concentration over a designated time interval.

Instantaneous Rate

The rate of change at a specific moment in time.

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Rate of Formation

The rate at which products are formed during a reaction.

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Rate of Consumption

The rate at which reactants are used up in a reaction.

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Relative Rates

The comparison of the rate of formation of products to the rate of consumption of reactants.

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Balanced Chemical Equation

An equation that shows equal numbers of atoms for each element on both sides.

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Study Notes

Chemical Kinetics: Reaction Rates

  • Respect Colleagues: Turn off cell phones, put aside personal materials, and refrain from using electronic devices (iPods, laptops, PDAs) for non-class-related activities during lectures and recitations.

General Chemistry II (Chem 1780-1) - January 22, 2025

  • Course: General Chemistry II (Chem 1780-1)
  • Date: Wednesday, January 22, 2025
  • Topic: Chemical Kinetics: Reaction Rates (Module 1)
  • Subtopic: Reaction Rates
    • Understanding the distinctions between rate of change, rate of consumption, and rate of formation.
    • Calculating relative rates using balanced chemical equations.
  • Next Topic: Kinetics: Rate laws; Method of Initial Rates
  • Assessments: Lecture Questions (Canvas; Due Jan 25 at 11:59 pm). OWL-01 and 02 (Saturday; single session only).

Average Reaction Rates

  • Definition: Average rate of change is calculated as the change in concentration over the change in time.
  • For a reaction A → D
  • Average rate of Change of D over first 30 minutes (Δ[D]/Δt) = +0.020 M/min
  • Average Rate of Change of A: (Δ[A]/Δt) = −0.020 M/min (negative because A is consumed).
  • Rate of Formation (Product): Positive (e.g., +0.020 M/min)
  • Rate of Consumption (Reactant): Negative (e.g., -0.020 M/min)

Instantaneous Reaction Rates

  • Definition: Instantaneous rate measures the reaction rate at a specific moment in time.
  • Representation: It’s represented by the instantaneous slope of the concentration vs. time graph, calculated as the derivative (d[D]/dt).
  • Positive slope D > 0: Formation of product.
  • Negative slope A < 0: Consumption of reactant.
  • Fastest rate: (time difference or dt) approaching zero (Δt → 0).

Relative Reaction Rates

  • Balanced Reactions: Essential for calculating relative rates (e.g., aA + bB → dD + eE).
  • Relationships: The relationship between the rates of consumption of reactants and the rates of formation of products are proportional to the stoichiometric coefficients in the balanced reaction.
  • Example: In the reaction: Ag⁺(aq) + 2CN⁻(aq) → [Ag(CN)₂]⁻(aq)
  • Rate of consumption of CN⁻(aq) = 2 * Rate of consumption of Ag⁺(aq)
    • Relative Rates = − 1/1 Δ[A]/Δt = − 1/2 Δ[CN⁻]/Δt

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