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61. Vapour pressures of water, acetone and ethanol at 293K are 2.34kPa, 12.36kPa and 5.85 kPa respectively. Which of these has the lowest and the highest boiling point? At 293K which of these evaporates least in a sealed container before equilibrium is established?

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Long Answer Type

62. State and explain the law of mass action.

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63. Apply the law of mass action to a reversible reaction and state the law of chemical equilibrium.

Let us consider a simple reversible reaction in the state of equilibrium

According to the law of mass action.
Rate of the forward reaction

where k_f is the rate constant for the forward reaction, [A] and [B] are molar concentrations of reactants A and B respectively.
Rate of the backward reaction (r_b) ∝ [C] [D] or r_b = k_b [C] [D]
where k_b is the rate constant for the backward reaction, [C] and [D] are molar concentrations of the products C and D respectively.
At equilibrium:
Rate of the forward reaction

= Rate of the backward reaction

The constant

is called equilibrium constant and has a constant value at a given temperature. Similarly, for a reaction

the above represents the complete expression for the law of chemical equilibrium. It may be defined as: For a reversible reaction at equilibrium, the ratio of the products of molar concentration of the products (substance formed) to the products of molar concentration of the reactants with each concentration term raised to a power equal to the number of moles of that substance in the balanced equation is constant at a given temperature.

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Short Answer Type

64. The equilibrium constant expression for a gas reaction is,

straight K subscript straight c space equals space fraction numerator open square brackets NH subscript 3 close square brackets to the power of 4 space open square brackets straight O subscript 2 close square brackets to the power of 5 over denominator open square brackets NO close square brackets to the power of 4 space open square brackets straight H subscript 2 straight O close square brackets to the power of 6 end fraction

Write the balanced chemical equation corresponding to this expression.

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65.

How is equilibrium constant expressed when the reaction is carried in the gaseous phase ?

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Long Answer Type

66. Derive the relation between K_p and K_c.

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67.

Under what conditions:
(i) K_p = K_c (ii) K_p> K_c (iii) K_p< K_c

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Short Answer Type

68.

Write the expressions for equilibrium constant for the reactions:
$left parenthesis straight i right parenthesis space straight H subscript 2 left parenthesis straight g right parenthesis space plus space space straight I subscript 2 left parenthesis straight g right parenthesis space space space space space rightwards harpoon over leftwards harpoon space space 2 HI left parenthesis straight g right parenthesis left parenthesis ii right parenthesis space straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space 2 NH subscript 3 left parenthesis straight g right parenthesis left parenthesis iii right parenthesis space PCl subscript 5 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space PCl subscript 3 left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis$

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69. Write equilibrium constant expression for the following:

left parenthesis straight i right parenthesis space Fe to the power of 3 plus end exponent left parenthesis aq right parenthesis space plus space SCN to the power of minus left parenthesis aq right parenthesis space space rightwards harpoon over leftwards harpoon space space FeSCN to the power of 2 plus end exponent left parenthesis aq right parenthesis left parenthesis ii right parenthesis space 3 Fe left parenthesis straight s right parenthesis space plus space 4 straight H subscript 2 straight O left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space Fe subscript 3 straight O subscript 4 left parenthesis straight s right parenthesis space plus space 4 straight H subscript 2 left parenthesis straight g right parenthesis

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70.

Write the expression for the equilibrium constant K_c for each of the following reactions:
$space 2 NOCl left parenthesis straight g right parenthesis space space space space space space space space space rightwards harpoon over leftwards harpoon space space space 2 NO left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis$

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