Chemical Equilibrium Basics
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Questions and Answers

When is equilibrium reached?

When, in a closed system, the rates of the forward and reverse reactions are occurring in equal rates and there is no change in concentration of reactants and products.

What is the equilibrium constant? (Symbol)

Kc

What is the law of chemical equilibrium?

At a given temperature, the ratio of the concentration of products (raised to power of their molar coefficient) to the concentration of the reactants (raised to the power of their molar coefficients) is a constant.

What does the magnitude of the equilibrium constant indicate?

<p>The extent of a reaction at equilibrium and its temperature dependence.</p> Signup and view all the answers

What is the reaction quotient? (Symbol)

<p>Q</p> Signup and view all the answers

What is the reaction quotient?

<p>The ratio of concentration of product to reactant.</p> Signup and view all the answers

What affects the position of equilibrium?

<p>Changes in concentration, pressure, and temperature.</p> Signup and view all the answers

Does a catalyst have an effect on the position of the equilibrium or equilibrium constant?

<p>False</p> Signup and view all the answers

What is dynamic equilibrium?

<p>The forward and reverse reactions continue but overall change in the concentration of reactants and products occurs.</p> Signup and view all the answers

Under what conditions will a saturated solution in a closed system establish a dynamic equilibrium?

<p>If there is excess solid present.</p> Signup and view all the answers

What happens at equilibrium?

<p>The forward and reverse reactions are occurring at equal rates, and can be approached from either forward or reverse reactions.</p> Signup and view all the answers

Does Kc have units?

<p>False</p> Signup and view all the answers

What does it mean if Kc is greater than 1?

<p>At a given temperature, products are favored over reactants.</p> Signup and view all the answers

What does a large Kc mean?

<p>The larger the value of Kc, the greater the proportion of products that exists compared with reactants at equilibrium.</p> Signup and view all the answers

What does a small Kc indicate?

<p>The reaction is unfavorable at this given temperature.</p> Signup and view all the answers

What happens in a homogenous equilibrium?

<p>All the reactants and products are present in one phase.</p> Signup and view all the answers

What happens in a heterogeneous equilibrium?

<p>The reactants or products exist in more than one phase.</p> Signup and view all the answers

What two points need to be considered when writing an equilibrium expression?

<p>(1) In an aqueous solution, water doesn't need to be included in Kc because its concentration doesn't change during the reaction. (2) If the reaction takes place in a non-aqueous solution, water must be included in Kc.</p> Signup and view all the answers

How do you find Kc for the forward reaction?

<p>Products over reactants.</p> Signup and view all the answers

How do you find Kc for the reverse reaction?

<p>Reactants over products.</p> Signup and view all the answers

What happens to Kc when the reaction is reversed?

<p>Inverse of the expression. (1/Kc)</p> Signup and view all the answers

What happens to Kc when the coefficients are halved?

<p>Square root of the expression (√Kc)</p> Signup and view all the answers

What happens to Kc when the coefficients are doubled?

<p>Square the reaction (Kc^2)</p> Signup and view all the answers

What happens to Kc when the change in reaction is the sum of equations?

<p>Product of the expressions. (Kc = Kc1 x Kc2 x...)</p> Signup and view all the answers

What happens to the equilibrium position and Kc when the concentration of products or reactants is changed?

<p>The equilibrium changes in response to a change in reactants or products. The Kc does not change.</p> Signup and view all the answers

What happens to the equilibrium position and Kc when the pressure is changed?

<p>Only with gaseous reactants, the equilibrium position is changed. The Kc does not change.</p> Signup and view all the answers

What happens to the equilibrium position and Kc when the temperature is changed?

<p>Usually changes: the direction of the change depends on whether the reaction is exothermic or endothermic. The Kc changes unless the Delta H = 0.</p> Signup and view all the answers

What happens to the equilibrium position and Kc when the catalyst is added?

<p>Nothing.</p> Signup and view all the answers

What is Le Chatelier's principle?

<p>If a change is made to a system that is in equilibrium, the balance between the forward and reverse reactions will shift to offset this change and return the system to equilibrium.</p> Signup and view all the answers

Would a change in concentration affect Kc?

<p>False</p> Signup and view all the answers

When considering the effect of changes in pressure on a reaction, which state of the reactants do you refer to?

<p>Only gaseous.</p> Signup and view all the answers

If the pressure of the system is increased, which way will the equilibrium shift? (the reactants have more moles)

<p>Reverse.</p> Signup and view all the answers

If the pressure of the system is decreased, which way will the equilibrium shift? (the reactants have more moles)

<p>Forward.</p> Signup and view all the answers

In an exothermic reaction, when the temperature is increased, how is the equilibrium position and equilibrium constant affected?

<p>The equilibrium position moves to the left, favoring reactants, and the equilibrium constant decreases.</p> Signup and view all the answers

In an exothermic reaction, when the temperature is decreased, how is the equilibrium position and equilibrium constant affected?

<p>The equilibrium position moves to the right, favoring products, and the equilibrium constant increases.</p> Signup and view all the answers

In an endothermic reaction, when the temperature is increased, how is the equilibrium position and equilibrium constant affected?

<p>The equilibrium position moves to the right, favoring products, and the equilibrium constant increases.</p> Signup and view all the answers

In an endothermic reaction, when the temperature is decreased, how is the equilibrium position and equilibrium constant affected?

<p>The equilibrium position moves to the left, favoring reactants, and the equilibrium constant decreases.</p> Signup and view all the answers

What does it mean if Q is greater than Kc?

<p>The concentration of products is greater than reactants at equilibrium and the reverse reaction is favored until equilibrium is reached.</p> Signup and view all the answers

What does it mean if Q is less than Kc?

<p>The concentration of reactants is greater than products at equilibrium and the forward reaction is favored until equilibrium is reached.</p> Signup and view all the answers

What does it mean if Q = Kc?

<p>The system is at equilibrium and the forward and reverse reactions occur at equal rates.</p> Signup and view all the answers

Study Notes

Equilibrium Basics

  • Equilibrium is achieved in a closed system when the forward and reverse reaction rates are equal, resulting in stable reactant and product concentrations.
  • Dynamic equilibrium means that while the sub-reactions continue, overall concentrations remain constant.

Equilibrium Constant and Reaction Quotient

  • The equilibrium constant is symbolized as Kc, representing the ratio of product to reactant concentrations at equilibrium.
  • The reaction quotient, denoted as Q, serves a similar purpose but is applicable at any point in the reaction, indicating whether the system is at equilibrium.

Factors Affecting Equilibrium

  • Equilibrium position can shift due to changes in concentration, pressure, and temperature.
  • A catalyst does not alter the position of equilibrium or the value of the equilibrium constant (Kc).

Laws and Principles of Chemical Equilibrium

  • According to the law of chemical equilibrium, the ratio of concentrations of products to reactants remains constant at a given temperature.
  • Le Chatelier's principle states that if a system at equilibrium experiences a change, the system will adjust to counteract that change, restoring balance.

Characteristics of Kc

  • Kc is dimensionless; it has no units.
  • A Kc greater than 1 indicates that products are favored, while a Kc less than 1 suggests reactants are favored.
  • The magnitude of Kc reflects the proportion of products to reactants at equilibrium.

Influence of Temperature on Equilibrium

  • In exothermic reactions, increasing temperature shifts the equilibrium to the left (favoring reactants), decreasing the Kc.
  • In endothermic reactions, increasing temperature shifts the equilibrium to the right (favoring products), increasing the Kc.

Reaction Coefficients and Kc Changes

  • Reversing a reaction inverses Kc (1/Kc).
  • Halving coefficients results in the square root of Kc (√Kc).
  • Doubling coefficients squares Kc (Kc²).
  • Adding reactions multiplies Kc values (Kc = Kc1 x Kc2 x...).

Concentration and Pressure Effects

  • Changes in concentration of reactants or products affect the equilibrium position but do not change Kc.
  • Pressure changes influence equilibrium positions only when gaseous reactants are present; Kc remains unchanged.

Understanding Equilibrium Conditions

  • A saturated solution establishes dynamic equilibrium when excess solid is present.
  • In heterogeneous equilibria, reactants and products exist in multiple phases, while homogenous equilibria involve only one phase.

Q vs Kc Interpretations

  • If Q > Kc, the reverse reaction is favored to reach equilibrium.
  • If Q < Kc, the forward reaction is favored to reach equilibrium.
  • Q = Kc indicates that the system is at equilibrium, with equal rates of forward and reverse reactions.

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Description

This quiz covers the fundamentals of chemical equilibrium, including equilibrium constants and reaction quotients. It discusses the factors that affect equilibrium positions and the principles governing dynamic equilibrium in closed systems. Test your understanding of these concepts and their applications.

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