Chemistry Reaction Rates and Equilibrium
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Questions and Answers

What is the primary function of a catalyst in a chemical reaction?

  • To increase the activation energy required for the reaction
  • To provide a source of energy for the reaction
  • To increase the speed of the reaction without being consumed (correct)
  • To undergo a chemical change during the reaction

Which type of catalyst operates in a different phase than the reactants?

  • Homogeneous catalyst
  • Biocatalyst
  • Autocatalyst
  • Heterogeneous catalyst (correct)

How will the rate of reaction change if the concentration of reactants A and B is increased three times in the equation Rate = k · [A]² · [B]?

  • Remains unchanged
  • Increases by 27 times (correct)
  • Increases by 6 times
  • Increases by 9 times

What effect does an inhibitor have on a chemical reaction?

<p>Increases the activation energy, slowing down the reaction (D)</p> Signup and view all the answers

In the equilibrium constant expression Kc = [NO]² · [O2] / [NO2]² for the reaction 2NO2 ⇌ 2NO + O2, what does a Kc value of 2.71 indicate?

<p>The reaction favors the formation of products (B)</p> Signup and view all the answers

What defines the reaction rate in a chemical reaction?

<p>The rate of change in concentration of reactants or products over time (A)</p> Signup and view all the answers

Which of the following factors is NOT a primary determinant of reaction rate?

<p>Total volume of the reaction vessel (A)</p> Signup and view all the answers

In a second-order reaction, which of the following rate laws is applicable?

<p>Rate = k[A]^2 (A)</p> Signup and view all the answers

What is the role of a catalyst in a chemical reaction?

<p>To increase the reaction speed without being consumed (B)</p> Signup and view all the answers

How does an increase in temperature affect the reaction rate?

<p>It increases the rate by providing more energy for molecular collisions (D)</p> Signup and view all the answers

What is activation energy (Ea) in the context of chemical reactions?

<p>The minimum energy required to initiate a chemical reaction (A)</p> Signup and view all the answers

According to the Arrhenius equation, which factor does NOT directly affect the rate constant (k)?

<p>Pressure of the surrounding environment (C)</p> Signup and view all the answers

What is the effect of increasing temperature on an endothermic reaction at equilibrium?

<p>Equilibrium shifts in the forward direction (B)</p> Signup and view all the answers

Which statement correctly describes the role of a catalyst in a chemical reaction?

<p>It lowers the activation energy and increases the rate of reaction. (C)</p> Signup and view all the answers

When Qc is less than Kc, what can be inferred about the reaction?

<p>The reaction shifts to the right towards products. (A)</p> Signup and view all the answers

What happens to the equilibrium position when pressure is decreased in a reaction with gaseous products?

<p>Equilibrium shifts to the side with more moles of gas. (D)</p> Signup and view all the answers

What does ΔH represent in a chemical reaction?

<p>The enthalpy change during the reaction (D)</p> Signup and view all the answers

Which statement about Le Chatelier's principle is true?

<p>Equilibrium shifts to minimize the effects of changes. (D)</p> Signup and view all the answers

What is the relationship between Kc and temperature for exothermic reactions when temperature is increased?

<p>Kc decreases as temperature increases. (A)</p> Signup and view all the answers

Which of the following statements correctly defines a dynamic equilibrium?

<p>Forward and reverse reactions occur at equal rates. (B)</p> Signup and view all the answers

How does removing a product from a reversible reaction at equilibrium affect Kc?

<p>Kc does not change. (A)</p> Signup and view all the answers

Flashcards

Reaction rate

The rate of change in concentration of reactants or products per unit time. Basically, how quickly or slowly a chemical reaction occurs.

Activation energy (Ea)

The minimum energy required to start a chemical reaction. It's like pushing a boulder uphill - you need initial energy to get it moving.

Catalyst

A substance that speeds up a reaction without being consumed itself. Imagine it as a matchmaker helping reactants 'meet' faster.

How concentration affects reaction rate

The higher the concentration of reactants, the faster the reaction. More particles mean more chances for collisions!

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How temperature affects reaction rate

Increasing temperature makes molecules move faster, increasing the rate of reaction. It's like heating up a pan - things cook faster at a higher temperature.

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Equilibrium

A state where the rates of forward and reverse reactions are equal, leading to no net change in concentration of reactants and products. Think of a tug-of-war where both teams pull equally.

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Le Chatelier's Principle

A principle that states that if a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress. Think of a seesaw - if you add weight to one side, it will tilt to balance.

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Homogeneous catalyst

A catalyst that exists in the same physical state (gas, liquid, or solid) as the reactants.

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Heterogeneous catalyst

A catalyst that exists in a different physical state than the reactants.

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Autocatalytic reaction

A reaction where one of the products acts as a catalyst for the same reaction.

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Inhibitor

A substance that slows down a reaction by increasing the activation energy.

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Chemical Equilibrium

A state where the rates of the forward and reverse reactions are equal, resulting in no net change in concentrations of reactants and products.

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Equilibrium Constant (Kc)

A constant that describes the ratio of products to reactants at equilibrium. For the reaction aA + bB <=> cC + dD, Kc = ([C]^c * [D]^d) / ([A]^a * [B]^b).

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Dynamic Equilibrium

The forward and reverse reactions continue to occur even at equilibrium, but at equal rates.

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Reaction Quotient (Qc)

A measure of the relative amounts of reactants and products at a given time. For the reaction aA + bB <=> cC + dD, Qc = ([C]^c * [D]^d) / ([A]^a * [B]^b).

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Effect of Concentration Change on Equilibrium

Adding reactant or removing product shifts the reaction towards the product side. Removing reactant or adding product shifts the reaction towards the reactant side.

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Effect of Temperature Change on Equilibrium

Increasing temperature favors the endothermic reaction, decreasing temperature favors the exothermic reaction.

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Effect of Catalyst on Equilibrium

A catalyst does not affect the position of equilibrium, it only speeds up the rate at which equilibrium is reached.

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Effect of Pressure Change on Equilibrium

Increasing pressure favors the side with fewer moles of gas. Decreasing pressure favors the side with more moles of gas.

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Study Notes

Reaction Rates and Equilibrium

  • Reaction rate measures how quickly reactant concentrations change over time.
  • Reaction rate is expressed as [product]/time or -[reactant]/time
  • Rate law describes the relationship between reaction rate and reactant concentrations.
  • First-order reaction rate depends linearly on one reactant concentration.
  • Second-order reaction rate depends on the square of one reactant concentration or on the product of the concentrations of two reactants.
  • Zero-order reaction rate is independent of reactant concentration.
  • Factors affecting reaction rate:
    • Concentration: Higher concentration generally leads to faster rates.
    • Temperature: Higher temperatures increase reaction rates.
    • Pressure (gases): Higher pressure generally increases reaction rates.
    • Surface area (solids): Larger surface areas lead to faster rates.
    • Catalysts: Catalysts speed up reactions by lowering activation energy without being consumed.
  • Activation energy (Ea): Minimum energy required to start a chemical reaction.

Chemical Equilibrium

  • Equilibrium is the state where the rates of forward and reverse reactions are equal.
  • Equilibrium constant (Kc): A constant that expresses the relationship between the concentrations of reactants and products at equilibrium.
  • Kc = [products]^coefficient / [reactants]^coefficient
  • Le Chatelier's Principle: If a system at equilibrium is perturbed (changed), the system will shift to counteract the change.

Equilibrium Shifts

  • Concentration changes: Adding reactants or removing products shifts equilibrium to favor product formation.
  • Temperature changes: Increasing the temperature favors the endothermic reaction; decreasing the temperature favors the exothermic reaction.
  • Pressure changes: Increasing pressure favors the side with fewer moles of gas.
  • Catalysts: Catalysts have no effect on the equilibrium position; they only affect the rate at which equilibrium is reached.

Reaction Quotient (Qc)

  • Reaction quotient (Qc): Similar to Kc, but calculated for any given set of concentrations, not just at equilibrium.
  • If Qc = Kc, the system is at equilibrium.
  • If Qc < Kc, the reaction will proceed to the right (toward products) to reach equilibrium.
  • If Qc > Kc, the reaction will proceed to the left (toward reactants) to reach equilibrium.

Catalysts

  • Heterogeneous catalysts: Catalysts in a different phase than the reactants.
  • Homogeneous catalysts: Catalysts in the same phase as the reactants.

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Description

This quiz covers the concepts of reaction rates, including factors that influence them, such as concentration, temperature, and pressure. Additionally, it explores the different types of reactions including first-order, second-order, and zero-order reactions. Test your understanding of how these elements interact in chemical reactions.

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