Chem 2 Chapter 15 Questions (Hard)
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Questions and Answers

Consider a reversible reaction at equilibrium. Which statement accurately describes the rates of the forward and reverse reactions?

  • The reverse reaction rate is significantly higher than the forward reaction rate.
  • The forward reaction rate is significantly higher than the reverse reaction rate.
  • The forward and reverse reaction rates are equal. (correct)
  • Both forward and reverse reactions have ceased.

How does a reaction at equilibrium differ from a reaction that has reached completion?

  • At equilibrium, all reactants have been converted to products, whereas a completed reaction still contains some reactants.
  • There is no difference; the terms are interchangeable.
  • At equilibrium, the rates of the forward and reverse reactions are equal, whereas a completed reaction proceeds only in the forward direction until all reactants are used up. (correct)
  • At equilibrium, the reaction has stopped, whereas a completed reaction is still ongoing.

Which statement accurately describes a system at dynamic equilibrium?

  • The concentrations of reactants and products are equal.
  • The rates of the forward and reverse reactions are zero.
  • The forward reaction has stopped, but the reverse reaction continues.
  • The rates of the forward and reverse reactions are constant and equal. (correct)

The equilibrium constant, K, for a reaction is 50. What can be inferred from this value?

<p>The reaction favors the products. (C)</p> Signup and view all the answers

What is the correct relationship among the equilibrium constants $K$, $K_c$, and $K_p$ for a given reaction?

<p>$K_c$ and $K_p$ are specific cases of $K$, using concentrations and pressures, respectively. (A)</p> Signup and view all the answers

Given the balanced chemical equation $aA + bB ightleftharpoons cC + dD$, which expression correctly represents the equilibrium constant K?

<p>$K = \frac{[C]^c[D]^d}{[A]^a[B]^b}$ (A)</p> Signup and view all the answers

For which states of matter are concentrations typically excluded from the equilibrium constant expression and why?

<p>Solids and pure liquids, because their concentrations remain essentially constant. (D)</p> Signup and view all the answers

How does the magnitude of the equilibrium constant, $K$, relate to the relative amounts of products and reactants at equilibrium?

<p>If $K$ is greater than 1, the amounts of products are greater than the amounts of reactants. (A)</p> Signup and view all the answers

Given the reaction $N_2(g) + 3H_2(g) ightleftharpoons 2NH_3(g)$ with equilibrium constant $K_1$, what is the equilibrium constant, $K_2$, for the reaction $2N_2(g) + 6H_2(g) ightleftharpoons 4NH_3(g)$?

<p>$K_2 = K_1^2$ (D)</p> Signup and view all the answers

If reaction 1 has an equilibrium constant of $K_1$ and reaction 2 has an equilibrium constant of $K_2$, what is the overall equilibrium constant $K_3$ if the two reactions are added together?

<p>$K_3 = K_1 \times K_2$ (D)</p> Signup and view all the answers

In an ICE table, what does the 'C' row represent, and how is it determined?

<p>The 'C' row represents the change in concentration and is determined using stoichiometric coefficients and a variable (e.g., x). (C)</p> Signup and view all the answers

How do you decide which direction the reaction will proceed in when constructing an ICE table?

<p>Reactions proceed in the direction that forms a reactant/product if there is an initial concentration of zero for that species. (C)</p> Signup and view all the answers

When using an ICE table to determine equilibrium concentrations, what is the significance of the variable 'x'?

<p>'x' represents the change in concentration needed to reach equilibrium. (D)</p> Signup and view all the answers

Which of the following can be determined using an ICE table?

<p>The concentrations of all species at equilibrium. (C)</p> Signup and view all the answers

What information is required to fully complete an ICE table with numerical values (no variables)?

<p>The initial concentrations of all species and the equilibrium concentration of at least one species are needed. (C)</p> Signup and view all the answers

What is the reaction quotient, Q, and how does it differ from the equilibrium constant, K?

<p>Q is calculated using initial concentrations, whereas K is calculated using equilibrium concentrations. (A)</p> Signup and view all the answers

If $Q > K$ for a reversible reaction, which of the following statements is correct?

<p>The reaction will shift to produce more reactants to reach equilibrium. (D)</p> Signup and view all the answers

If $Q < K$ for a reversible reaction, how will the system adjust to reach equilibrium?

<p>The system will shift to produce more products. (A)</p> Signup and view all the answers

According to Le Châtelier's Principle, what happens to a system at equilibrium when conditions change?

<p>The system shifts to counteract the change and establish a new equilibrium. (C)</p> Signup and view all the answers

For the exothermic reaction $A(g) ightleftharpoons B(g) + heat$, how will increasing the temperature affect the equilibrium position?

<p>It will shift the equilibrium to the left, favoring reactant formation. (A)</p> Signup and view all the answers

How does adding an inert gas (one that does not participate in the reaction) at constant volume affect a system at equilibrium?

<p>It has no effect on the equilibrium position. (B)</p> Signup and view all the answers

How does a catalyst affect the equilibrium of a reversible reaction?

<p>It does not affect the equilibrium position. (A)</p> Signup and view all the answers

Consider the reaction $2SO_2(g) + O_2(g) ightleftharpoons 2SO_3(g)$. If the volume of the container is decreased, how will the equilibrium be affected?

<p>The equilibrium will shift to the right, favoring the products. (A)</p> Signup and view all the answers

For an endothermic reaction, how does decreasing the temperature affect the equilibrium position?

<p>It shifts the equilibrium towards the reactants. (B)</p> Signup and view all the answers

What is incorrect about the statement: 'Once a reaction reaches equilibrium, the reaction stops'?

<p>At equilibrium, the rates of the forward and reverse reactions are equal, but both reactions continue. (A)</p> Signup and view all the answers

Why doesn't a catalyst change the position of equilibrium?

<p>A catalyst speeds up both the forward and reverse reactions equally. (A)</p> Signup and view all the answers

Consider a reaction that is at equilibrium. Which of the following statements is true regarding the concentrations of reactants and products?

<p>The concentrations of reactants and products are constant. (A)</p> Signup and view all the answers

You are given the initial concentrations of reactants and products, along with the equilibrium constant, K. What is the primary purpose of using an ICE table in this scenario?

<p>To calculate the equilibrium concentrations of reactants and products. (D)</p> Signup and view all the answers

When is the reaction quotient (Q) equal to the equilibrium constant (K)?

<p>When the reaction is at equilibrium. (A)</p> Signup and view all the answers

Flashcards

Chemical Equilibrium

Forward and reverse reactions occur at the same rate, maintaining constant reactant and product amounts.

Equilibrium vs. Completion

Equilibrium is dynamic with ongoing reactions; completion means all reactants convert to products.

Characteristics of Equilibrium

Rates of forward and reverse reactions are equal; reactions continue; reactant and product amounts are constant.

Equilibrium Constant (K)

K is the ratio of product to reactant concentrations at equilibrium, indicating reaction progress.

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K, Kc, and Kp

K is general; Kc uses concentration units; Kp uses pressures; others apply in specific circumstances.

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Writing K Expression

Products' concentrations (raised to coefficients) over reactants' concentrations (raised to coefficients).

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States Excluded from K

Solids and pure liquids aren't included because their concentrations don't change during the reaction.

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K Value and Reaction Direction

K > 1 favors products; K < 1 favors reactants; K ≈ 1 means roughly equal amounts.

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Manipulating Keq

If you multiply a reaction by a coefficient, raise the equilibrium constant to the power equal to that coefficient. If you reverse reactions, take the reciprocal of the equilibrium constant.

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Adding Reactions and K

K3 is K₁ and K2 multiplied together. If you add reactions, multiply their equilibrium constants.

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ICE Table Problem Types

Type 1 finds equilibrium concentrations; Type 2 finds the equilibrium constant K;.

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Reaction Quotient (Q)

Q predicts reaction direction by comparing current concentrations to K.

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Q and Reaction Shift

Q < K favors products (forward); Q > K favors reactants (reverse).

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Steps to Calculate Equilibrium Concentrations

  1. Set up ICE table 2. Determine changes in concentration 3. Write the expression for K 4. Solve for x 5. Calculate equilibrium concentrations
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Le Châtelier's Principle

A system at equilibrium adjusts to counteract changes, restoring a new equilibrium.

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Concentration Changes and Equilibrium

Adding a reactant shifts the reaction to the right. Removing a reactant shifts the reaction to the left. Adding a product shifts the reaction to the left. Removing a product shifts the reaction to the right.

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Volume Changes and Equilibrium

Decrease volume, shift to side with fewer moles of gas; increase volume, shift to side with more.

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Temperature Changes & Equilibrium

Increase T for endothermic, shift right; decrease T, shift left. Increase T for exothermic, shift left; decrease T, shift right.

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Equilibrium Misconception

Reactants still turn into products, and products still turn back into reactants, but they do so at the same rate. This is why the concentrations stay constant.

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Catalyst and Equilibrium

A catalyst speeds up both the forward and reverse reactions equally, which helps the reaction reach equilibrium faster. However, it doesn't change the amounts of reactants and products at equilibrium, so the position of equilibrium stays the same.

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Study Notes

The Equilibrium Constant

  • Chemical equilibrium occurs when forward and reverse reactions proceed at the same rate.
  • At equilibrium, reactants turn into products as quickly as products revert to reactants.
  • Amounts of reactants and products remain constant at equilibrium, though the reaction continues.
  • Equilibrium differs from completion; reactions at equilibrium are ongoing but balanced.
  • Reactions that reach completion have converted all reactants to products and then stop.
  • At equilibrium, forward and reverse reaction rates are equal.
  • Dynamic equilibrium means forward and reverse reactions continue.
  • At equilibrium, the amounts of reactants and products stay constant.
  • The equilibrium constant (K) is the ratio of product to reactant concentrations at equilibrium.
  • K indicates how far a reaction proceeds toward product formation.
  • A large K means the reaction creates many products.
  • A small K indicates the reaction produces few products, and more reactants are present.
  • K is the general equilibrium constant
  • Kc uses concentration units
  • Kp uses pressure units.
  • To express K, product concentrations are raised to the power of their coefficients, multiplied, and divided by the same process applied to reactant concentrations.
  • Products are in the numerator, and reactants in the denominator.
  • Solids and pure liquids aren't included in the K expression.
  • Their concentrations remain constant and don't affect equilibrium.
  • Kc is greater than 1 when there are more products than reactants.
  • Kc is less than 1 when there are more reactants than products.
  • K is close to 1 when product and reactant amounts are roughly equal.
  • When a reaction is multiplied by a coefficient, raise K1 to the power of that coefficient to find K2
  • If a reaction is reversed, take the reciprocal of K2 to find K3
  • K3 is K1 multiplied by K2 if reactions are added

Using ICE Tables and Q

  • ICE tables solve equilibrium problems.
  • Type 1 problems provide initial concentrations and K.
  • Use the ICE table and K to solve for 'x' to find equilibrium concentrations.
  • Variable 'x' represents changes in concentration within the ICE table.
  • Type 2 problems provide initial and equilibrium concentrations.
  • Completely fill out the ICE table to calculate K.
  • Both types use ICE tables to organize concentration changes and require writing an equilibrium constant expression.
  • Type 1 problems don't provide enough information to complete the ICE table without 'x.'
  • Type 2 problems can be fully completed with given values.
  • The reaction quotient, Q, uses current concentrations instead of equilibrium concentrations.
  • Q predicts the direction a reaction will shift to reach equilibrium.
  • If Q < Kc, the system makes more products (proceeds forward).
  • If Q > Kc, the system makes more reactants (proceeds in reverse).
  • To calculate equilibrium concentrations:
    • Use molarities to write all initial concentrations in an ICE table.
    • Use 'x' to represent concentration changes in the 'C' row. Reaction direction matters; a zero initial concentration means the reaction must proceed in that direction.
    • The balanced equation is used to write the K expression with equilibrium concentrations. Substitute values from the ICE table into the K expression and solve for 'x.'
    • Use 'x' to calculate equilibrium concentrations for all species.

Le Chatelier

  • Le Châtelier's Principle: a system at equilibrium responds to counteract changes in concentration, temperature, or pressure, restoring a new equilibrium.
  • Add a reactant, the reaction shifts right.
  • Remove a reactant, the reaction shifts left.
  • Add a product, the reaction shifts left.
  • Remove a product, the reaction shifts right.
  • Decrease volume, shifts to the side with fewer moles of gas.
  • Increase volume, shifts to the side with more moles of gas.
  • Increase temperature for an endothermic reaction, shifts right.
  • Decrease temperature for an endothermic reaction, shifts left.
  • Increase temperature for an exothermic reaction, shifts left.
  • Decrease temperature for an exothermic reaction, shifts right.
  • Adding a catalyst causes no change.
  • At equilibrium, reactants and products interconvert at the same rate, maintaining constant concentrations.
  • Catalysts speed up forward and reverse reactions equally.
  • Catalysts help reactions reach equilibrium faster without changing equilibrium positions.

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Understand chemical equilibrium where forward and reverse reactions occur at the same rate, leading to constant reactant and product amounts. Learn how the equilibrium constant (K) indicates the extent of product formation; a large K favors products, while a small K favors reactants. Explore dynamic equilibrium where reactions continue, but rates are balanced.

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