Calcium carbonate decomposes upon heating according to the balanced equation A rigid

CHEMISTRY · Multi-part · A Level · Chemistry · Gaseous equilibria (Kp) · Gaseous equilibria (Kp)

Problem

Calcium carbonate decomposes upon heating according to the balanced equation

\mathrm{CaCO_{3}}(s) \rightleftharpoons \mathrm{CaO}(s) + \mathrm{CO_{2}}(g)

A rigid, evacuated

4.00\,\text{L}

vessel is charged with excess powdered

\mathrm{CaCO_{3}}

and heated to

825\,\text{K}

until equilibrium is established. After equilibrium is reached, the partial pressure of

\mathrm{CO_{2}}

in the vessel is measured to be

0.242\,\text{atm}

. (1) Part 1: (a) Write the expression for the equilibrium constant

K_p

for this reaction and clearly state which species, if any, are omitted from the expression. (2) Part 2: (b) Explain, in terms of the properties of the phases present, why any species you omitted in part (a) do not appear in the equilibrium‐constant expression. (3) Part 3: (c) Calculate the numerical value of

K_p

825\,\text{K}

for this decomposition. (4) Part 4: (d) The literature value of

K_p

for this system at

825\,\text{K}

0.256\,\text{atm}

. Identify two possible experimental factors that could account for the small difference between your calculated value in part (c) and the literature value, and briefly describe how each factor would influence the measured pressure.

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