Skip to main content
Pearson+ LogoPearson+ Logo
Ch.15 - Chemical Equilibrium
All textbooksBrown 15th EditionCh.15 - Chemical EquilibriumProblem 17
Chapter 15, Problem 17

When the following reactions come to equilibrium, does the equilibrium mixture contain mostly reactants or mostly products? (a) N2(g) + O2(g) ⇌ 2 NO(g), Kc = 1.5 × 10^-10 (b) 2 SO2(g) + O2(g) ⇌ 2 SO3(g), Kp = 2.5 × 10^9

Verified step by step guidance
1
Step 1: Understand the concept of equilibrium constant (K). The equilibrium constant (K) is a measure of the extent of a reaction at equilibrium. A large K value (K >> 1) indicates that the reaction favors the formation of products, while a small K value (K << 1) indicates that the reaction favors the formation of reactants.
Step 2: Analyze reaction (a) N2(g) + O2(g) ⇌ 2 NO(g) with Kc = 1.5 × 10^-10. Since Kc is much less than 1, this suggests that at equilibrium, the concentration of reactants (N2 and O2) is much greater than the concentration of products (NO).
Step 3: Conclude for reaction (a) that the equilibrium mixture contains mostly reactants because the equilibrium constant is very small, indicating the reaction does not proceed far towards products.
Step 4: Analyze reaction (b) 2 SO2(g) + O2(g) ⇌ 2 SO3(g) with Kp = 2.5 × 10^9. Since Kp is much greater than 1, this suggests that at equilibrium, the concentration of products (SO3) is much greater than the concentration of reactants (SO2 and O2).
Step 5: Conclude for reaction (b) that the equilibrium mixture contains mostly products because the equilibrium constant is very large, indicating the reaction proceeds significantly towards products.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Chemical Equilibrium

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. At this point, the system is dynamic, meaning that reactions continue to occur, but there is no net change in the concentrations of the substances involved.
Recommended video:
Guided course
04:21
Chemical Equilibrium Concepts

Equilibrium Constant (K)

The equilibrium constant (K) quantifies the ratio of the concentrations of products to reactants at equilibrium for a given reaction at a specific temperature. A large K value (much greater than 1) indicates that products are favored at equilibrium, while a small K value (much less than 1) suggests that reactants are favored.
Recommended video:
Guided course
01:14
Equilibrium Constant K

Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is disturbed by changes in concentration, temperature, or pressure, the system will adjust to counteract the disturbance and restore a new equilibrium. This principle helps predict how changes will affect the position of equilibrium in a reaction.
Recommended video:
Guided course
07:32
Le Chatelier's Principle
Related Practice
Textbook Question

Write the expression for Kc for the following reactions. In each case indicate whether the reaction is homogeneous or heterogeneous.

(a) 3 NO(g) ⇌ N2O(g) + NO2(g)

(b) CH4(g) + 2 H2S(g) ⇌ CS2(g) + 4 H2(g)

(c) Ni(CO)4(g) ⇌ Ni(s) + 4 CO(g)

(d) HF(aq) ⇌ H+(aq) + F-(aq)  

(e) 2Ag(s) + Zn2+(aq) ⇌ 2 Ag+(aq) + Zn(s)

(f) H2O(l) ⇌ H+(aq) + OH-(aq)

(g) 2 H2O(l) ⇌ 2 H+(aq) + 2 OH-(aq)

Textbook Question

Write the expressions for Kc for the following reactions. In each case indicate whether the reaction is homogeneous or heterogeneous.

(a) 2 O3(g) ⇌ 3 O2(g)

(c) 2 C2H4(g) + 2 H2O(g) ⇌ 2 C2H6(g) + O2(g)

(d) C(s) + 2 H2(g) ⇌ CH4(g)

(e) 4 HCl(aq) + O2(g) ⇌ 2 H2O(l) + 2 Cl2(g)

(f) 2 C8H18(l) + 25 O2(g) ⇌ 16 CO2(g) + 18 H2O(g)

(g) 2 C8H18(l) + 25 O2(g) ⇌ 16 CO2(g) + 18 H2O(l)

Textbook Question

Write the expressions for 𝐾𝑐 for the following reactions. In each case indicate whether the reaction is homogeneous or heterogeneous.

(b) Ti(𝑠) + 2Cl2(𝑔) ⇌ TiCl4(𝑙)

Textbook Question

Which of the following reactions lies to the right, favoring the formation of products, and which lies to the left, favoring the formation of reactants?

(a) 2 NO(g) + O2(g) ⇌ 2 NO2(g) Kp = 5.0 × 1012

(b) 2 HBr(g) ⇌ H2(g) + Br2(g) Kc = 5.8×10−18

Textbook Question

Which of the following statements are true and which are false? (c) As the value of the equilibrium constant increases, the speed at which a reaction reaches equilibrium must increase.