Book cover for Objective Chemistry for Engineering and Medical Entrance Examinations

Objective Chemistry for Engineering and Medical Entrance Examinations

K Rama Rao

ISBN #9789332541771

1st Edition

2,463 Questions

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12,716 Students Helped

Homework Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

Chemical equilibrium is a dynamic state in reversible reactions where the forward and backward reaction rates are equal, leading to constant concentrations of reactants and products. Understanding the differences between reversible and irreversible reactions, the role of reaction conditions, and how equilibrium can be shifted is essential for controlling chemical processes both in the laboratory and industrial settings.

Learning Objectives

1

Describe the fundamentals of chemical reactions including reversible and irreversible processes.

2

Explain the concept of chemical equilibrium and how the rates of forward and backward reactions equalize.

3

Identify the roles of reactants and products in a chemical reaction.

4

Analyze the effects of reaction conditions and product removal on the equilibrium state.

Key Concepts

CONCEPT

DEFINITION

Chemical Equilibrium

A state in a reversible reaction where the rate of the forward reaction equals the rate of the backward reaction, resulting in constant concentrations of reactants and products.

Reversible Reaction

A chemical reaction where the reactants form products and the products can revert back to the reactants under the given conditions.

Irreversible Reaction

A chemical reaction that proceeds in only one direction, where products do not convert back to reactants under normal conditions.

Rate of Reaction

The speed at which reactants are converted into products, influenced by factors such as temperature, concentration, and catalysts.

Reactants

Substances that start a reaction and are consumed during the process of the chemical reaction.

Products

Substances that are formed as a result of the chemical reaction.

Reaction Conditions

External factors such as temperature, pressure, and concentration that affect the rate and equilibrium state of a chemical reaction.

Example Problems

Example 1

Which of the following statemcnts is false about when a chemical reaction is in equilibrium? (1) The rate of forward and backward reactions is equal (2) Concentrations of all substances are constant (3) For a reaction in a gaseous state to reach equilibrium the reaction should be carried out in closed vessel (4) The ratio of the product of the mass of products and that of reactants varies continuously.

Example 2

In lime kiln, the reversible reaction $\mathrm{CaCO}_{3}(\mathrm{~s}) \rightleftharpoons$ $\mathrm{CaO}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{~g})$ proceeds to completion because (1) of high temperature (2) $\mathrm{CO}_{2}$ escapes out (3) $\mathrm{CaO}$ is removed (4) of low pressure

Example 3

A chemical reaction is in equilibrium. Addition of a catalyst would not result in (1) the rates of forward and backward reactions are equally altered (2) a new reaction pathway to reaction (3) attainment of equilibrium quickly (4) increase in the amount of heat evolved in the reaction

Example 4

\Lambdall reactions involving chemical decomposition are (1) Reversible (2) Reversible and endothermic (3) Exothermic (4) May be reversible or irreversible and endothermic or exothermic

Example 5

$\Lambda$ cylindcr fitted with a movable piston contains liquid water in cquilibrium with water vapour at $25^{\circ} \mathrm{C}$. Which opcration results in a decrcase in the cquilibrium vapour pressure? (1) Moving the piston downward a short distancc (2) Removing a small amount of vapour (3) Removing a small amount of the liquid (4) Dissolving the salt in water
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Step-by-Step Explanations

QUESTION

How does a reversible chemical reaction reach equilibrium?

STEP-BY-STEP ANSWER:

Step 1: Identify the forward reaction (reactants to products) and its rate, as well as the reverse reaction (products to reactants) and its rate.
Step 2: Monitor the changes in concentration of reactants and products over time as the reaction proceeds.
Step 3: Recognize that as the reaction progresses, the rate of the forward reaction decreases while the rate of the reverse reaction increases due to the changing concentrations.
Step 4: Observe that equilibrium is reached when the rate of the forward reaction equals the rate of the reverse reaction; at this point, the concentrations of reactants and products remain constant.
Final Answer: A reversible reaction reaches equilibrium when the forward and reverse reactions occur at the same rate, leading to stable concentrations of reactants and products.

Chemical Equilibrium

QUESTION

How do changes in reaction conditions affect chemical equilibrium?

STEP-BY-STEP ANSWER:

Step 1: Identify the factors that influence reaction conditions, such as temperature, pressure, and concentration of reactants or products.
Step 2: Understand that altering these conditions can shift the equilibrium position by favoring either the forward or reverse reaction.
Step 3: Recognize that removal of a product from the system reduces its concentration, shifting the equilibrium to produce more product in order to restore balance.
Step 4: Apply the concept of Le Chatelier's Principle, which predicts how a system at equilibrium responds to changes in conditions.
Final Answer: Changes in reaction conditions like temperature, pressure, and reactant/product concentrations can shift the equilibrium position by favoring reaction processes that counteract the change.

Effect of Reaction Conditions

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Common Mistakes

  • Confusing chemical equilibrium with a static state, rather than a dynamic balance of rates.
  • Assuming that all reactions are reversible without considering the conditions that enable the backward reaction.
  • Overlooking the impact of external factors like concentration changes and temperature on shifting the equilibrium.
  • Misunderstanding the role of product removal, thinking it stops the reaction rather than shifting the equilibrium.