Q19 of 73 Page 224

A sample of pure PCl5 was introduced into an evacuated vessel at 473 K. After equilibrium was attained, concentration of PCl5 was found to be 0.5 × 10–1 mol L–1. If value of Kc is 8.3 × 10–3, what are the concentrations of PCl3 and Cl2 at equilibrium?

PCl5 (g) ⇌ PCl3 (g) + Cl2(g)

For the given reaction, let’s assume that the initial molar concentration of PCl5 is x mol/L.

The given reaction is:



Moles of PCl5 decomposed during the reaction=Moles of PCl3 formed=Moles of Cl2 formed=(x-0.05) mol/L


Equilibrium constant (Kc) is defined as a number that expresses the relationship between the amounts of products and reactants present at equilibrium in a reversible chemical reaction at a given temperature.


Here, Kc = 0.0083


For the given reaction,



Where, [PCl3] = concentration of PCl3 in mol/L at equilibrium


[Cl2] = concentration of Cl2 in mol/L at equilibrium


[PCl5] = concentration of PCl5 in mol/L at equilibrium



(x-0.05)2 = 0.000415


(x-0.05) = 0.0203


x = 0.07 mol/L


Therefore, [PCl3] = (x-0.05) = 0.07-0.05 = 0.02 mol/L


[Cl2] = (x-0.05) = 0.07-0.05 = 0.02 mol/L


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Kp= 0.04 atm at 899 K for the equilibrium shown below. What is the equilibrium concentration of C2H6 when it is placed in a flask at 4.0 atm pressure and allowed to come to equilibrium?

C2H6 (g) ⇌ C2H4 (g) + H2 (g)

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Ethyl acetate is formed by the reaction between ethanol and acetic acid and the equilibrium is represented as:

CH3COOH (l) + C2H5OH (l) ⇌CH3COOC2H5 (l) + H2O (l)


(i) Write the concentration ratio (reaction quotient), Qc, for this reaction (note: water is not in excess and is not a solvent in this reaction)


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(iii) Starting with 0.5 mol of ethanol and 1.0 mol of acetic acid and maintaining it at 293 K, 0.214 mol of ethyl acetate is found after sometime. Has equilibrium been reached?

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One of the reaction that takes place in producing steel from iron ore is the reduction of iron(II) oxide by carbon monoxide to give iron metal and CO2.

FeO (s) + CO (g) ⇌ Fe (s) + CO2 (g); Kp = 0.265 atm at 1050K


What are the equilibrium partial pressures of CO and CO2 at 1050 K if the initial partial pressures are: = 1.4 atmand = 0.80 atm?

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Equilibrium constant, Kcfor the reaction

N2 (g) + 3H2 (g) ⇌ 2NH3 (g) at 500 K is 0.061


At a particular time, the analysis shows that composition of the reaction mixture is 3.0 mol L–1 N2, 2.0 mol L–1 H2 and 0.5 mol L–1 NH3. Is the reaction at equilibrium?


If not in which direction does the reaction tend to proceed to reach equilibrium?