Phosgene (COCl ) can undergo further chlorination in two sequential reversible steps…

CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)

Problem

Phosgene (COCl

_2

) can undergo further chlorination in two sequential reversible steps at a given temperature: Step 1: CO(g) + Cl

_2

(g) ⇌ COCl

_2

(g)

K_{c1} = 4.8 \times 10^{3}

Step 2: COCl

_2

(g) + Cl

_2

(g) ⇌ COCl

_4

(g)

K_{c2} = 5.1 \times 10^{2}

(a) Write the equilibrium‐constant expression

K_{c1}

for Step 1 and

K_{c2}

for Step 2. (b) Derive the equilibrium‐constant expression for the overall reaction CO(g) + 2 Cl

_2

(g) ⇌ COCl

_4

(g) in terms of

K_{c1}

and

K_{c2}

, and calculate the numerical value of the overall constant

K_{c,\text{overall}}

at this temperature. (c) Explain, citing the law of mass action, why the numerical value obtained in part (b) can be interpreted as the product of the two individual constants.

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