13. Basic Chemistry: Chemical Equilibrium

Calculate the equilibrium constant (K_c) for the given reaction and tell whether equilibrium lies to the left or the right. PCl_{5 (g)} ↔ PCl_{3 (g)} + Cl_{2 (g)}

Equilibrium concentrations are: [PCl₅] = 0.25 M, [PCl₃] = 9.7 × 10^-4 M, and [Cl₂] = 3.2 × 10^-3 M.

• Kc = 2.5 × 10^-3; equilibrium lies to the right.

• Kc = 5.0 × 10^-6; equilibrium lies to the right.

• Kc = 3.2 × 10^-2; equilibrium lies to the left.

• Kc = 1.24 × 10^-5; equilibrium lies to the left.

• Kc = 1.0 × 10^-4; equilibrium lies to the left.

What is the K_c expression for this reaction?
   2NO_(g)  +  O_2(g) ⇌  2NO_2(g)

• Kc = [NO₂]² / ([NO]² x [O₂])

• Kc = [NO]² x [O₂] / [NO₂]²

• Kc = [NO₂] / ([NO]² x [O₂])

• Kc = [O₂] / ([NO]² x [NO₂]²)

• Kc = [NO]² / ([NO₂]² x [O₂])

When 0.40 mole of SO₂ and 0.60 mole of O₂ are placed in an evacuated 1.00–liter flask, the reaction represented below occurs.

2SO_{2 (g)} + O_{2 (g)} ↔ 2SO_{3 (g)}

After the reactants and the product reach equilibrium and the initial temperature is restored, the flask is found to contain 0.30 mole of SO₃. Based on these results, the equilibrium constant, K_c, for the reaction is ..................

• 20
• 1.5

• 30
• 10
• 2.5

H_2(g) + Cl_2(g) ⇌ 2HCl_(g)

The forward reaction is exothermic. What will happen to the equilibrium if the temperature is increased?

• The concentration of H₂ will not change.

• The equilibrium will shift to the right, favoring HCl.
• The reaction will stop completely.
• The equilibrium will shift to the left, favoring H₂ and Cl₂.

• The equilibrium will remain unchanged.

What is the equilibrium expression (K_c) for this reaction?

Fe₃O_4(s) + 4H_2(g) ⇌ 3Fe_(s) + 4H₂O_(g)

• Kc = [Fe]³ [H₂O]⁴  / [Fe₃O₄] [H₂]⁴

• Kc = [Fe₃O₄] [H₂]⁴ /  [Fe]³ [H₂O]⁴

• Kc = [H₂]⁴ / [Fe]³

• Kc = [Fe] [H₂O] / [Fe₃O₄] [H₂]

• Kc = [H₂O]⁴ / [H₂]⁴

What are the two factors to look for when determining if the reaction is at equilibrium?

• Constant concentrations and equal reaction rates.
• Fluctuating concentrations and varying reaction rates.
• Constant temperature and pressure changes.
• Forward reaction rate is faster than the reverse and concentrations are equal

• Increased volume and decreased pressure.

2SO_2(g) + O_2(g) ⇌ 2SO_3(g)
Removing O_2(g) will ............

• shift the equilibrium to the left
• shift the equilibrium to the right
• produce more SO₃

• increase the concentration of SO₂

• decrease the temperature

For the reaction N_{2 (g)} +  3 H_2 (g) ⇌ 2 NH_{3 (g)}

If the pressure in the system is increased,  which substance(s) will increase in concentration?

• N₂ and H₂

• H₂

• no change in substances

• NH₃

• N₂

When the rate of the forward reaction is equal to the rate of backward reaction, the system is said to be in ...............

• reaction
• stoichiometry

• stability
• balance

• equilibrium

Which chemical species is the reactant and why?

• A, as concentration decreases

• A and B, as concentration remains unchanged.

• A, as concentration increases

• B, as concentration decreases

• B, as concentration increases