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NEET-XI-Chemistry

06: Chemical Thermodynamics

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  • #19
    For the reaction

    2A(g) + B(g) → 2D(g)

    ΔUθ = -10.5 kJ and ΔSθ= -44.1 JK-1.

    Calculate ΔGθ for the reaction, and predict whether the reaction may occur spontaneously.
    Ans : For the given reaction,

    2 A(g) + B(g) → 2D(g)

    Δng = 2 - (3)

    = -1 mole

    Substituting the value of ΔUθ in the expression of ΔH:

    ΔHθ = ΔUθ + ΔngRT

    = (-10.5 kJ) - (-1) (8.314 × 10-3 kJ K-1 mol-1) (298 K)

    = -10.5 kJ - 2.48 kJ

    ΔHθ = -12.98 kJ

    Substituting the values of ΔHθ and ΔSθ in the expression of ΔGθ:

    ΔGθ = ΔHθ - TΔSθ

    = -12.98 kJ - (298 K) (-44.1 J K-1)

    = -12.98 kJ + 13.14 kJ

    ΔGθ = + 0.16 kJ

    Since ΔGθ for the reaction is positive, the reaction will not occur spontaneously.