Aim for FiveChemistry

Short free-response question

Nitrosyl chloride: a small equilibrium constant

  • Unit 7
  • 4 points
  • About 9 minutes

You can use a calculator on this question, just like on exam day.

A shorter multipart question that sticks to one or two topics. Each part usually asks for one calculation, claim or explanation. On the exam: 4 questions (Questions 4–7), part of the 1-hour-45-minute free-response section; calculator allowed.

The question

Nitrosyl chloride decomposes reversibly: 2 NOCl(g) ⇌ 2 NO(g) + Cl₂(g). At a certain temperature, Kc = 1.6 × 10⁻⁵.

Suggested time: 9 minutes

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Part (a)

1 point

Calculate the value of Kc for the reaction 4 NO(g) + 2 Cl₂(g) ⇌ 4 NOCl(g) at the same temperature.

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Part (b)

1 point

At the same temperature, 2 NO(g) + O₂(g) ⇌ 2 NO₂(g) has Kc = 4.0 × 10³ (a hypothetical value for this question). Calculate Kc for the reaction 2 NOCl(g) + O₂(g) ⇌ 2 NO₂(g) + Cl₂(g).

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Part (c)

1 point

A sample of NOCl(g) with an initial concentration of 0.50 M is placed in an otherwise empty, rigid container and allowed to reach equilibrium at the same temperature. Calculate [Cl₂] at equilibrium.

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Part (d)

1 point

Justify the approximation that [NOCl] at equilibrium is essentially equal to 0.50 M, using both the magnitude of Kc and your answer to part (c).

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