For a reaction to be spontaneous at all temperatures, the values of enthalpy change $\Delta H$ and entropy change $\Delta S$ should be:

  • A
    $\Delta H > 0$ and $\Delta S > 0$
  • B
    $\Delta H < 0$ and $\Delta S > 0$
  • C
    $\Delta H < 0$ and $\Delta S < 0$
  • D
    $\Delta H > 0$ and $\Delta S < 0$

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Calculate the amount of work done during isothermal expansion of a gas from a volume of $4 \ dm^{3}$ to $6 \ dm^{3}$ against a constant external pressure of $3 \ atm$ (in $J$)?

The standard state Gibbs free energies of formation of $C$ (graphite) and $C$ (diamond) at $T = 298 \ K$ are:
$\Delta_f G^0[C(\text{graphite})] = 0 \ kJ \ mol^{-1}$
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The standard state means that the pressure should be $1 \ bar$,and the substance should be pure at a given temperature. The conversion of graphite [$C$ (graphite)] to diamond [$C$ (diamond)] reduces its volume by $2 \times 10^{-6} \ m^3 \ mol^{-1}$. If $C$ (graphite) is converted to $C$ (diamond) isothermally at $T = 298 \ K$,the pressure at which $C$ (graphite) is in equilibrium with $C$ (diamond) is:
[Useful information: $1 \ J = 1 \ kg \ m^2 \ s^{-2} ; 1 \ Pa = 1 \ kg \ m^{-1} \ s^{-2} ; 1 \ bar = 10^5 \ Pa$ ] (in $bar$)

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