For the reaction $A \to B$,$\Delta H = 4 \, kcal \, mol^{-1}$ and $\Delta S = 10 \, cal \, K^{-1} \, mol^{-1}$. At what temperature $(K)$ will the reaction become spontaneous?

The standard enthalpy for the decomposition of $N_2O_5$ to $NO_2$ is $58.04 \ kJ$ and standard entropy of this reaction is $176.7 \ J/K$. The standard free energy change for this reaction at $25 \ ^oC$ is .................. $kJ$.

For the reaction $CaCO_3(s) \rightarrow CaO(s) + CO_2(g)$ at $298 \ K$ and $1 \ atm$ pressure,the values of $\Delta H^o$ and $\Delta S^o$ are $+179.1 \ kJ \ mol^{-1}$ and $+160.2 \ J \ K^{-1} \ mol^{-1}$ respectively. Assuming that $\Delta H^o$ and $\Delta S^o$ do not change with temperature,at what temperature (in $K$) will the process become spontaneous?

Under what conditions will a reaction become spontaneous at all temperatures?

For the oxidation of ammonia at $298 \ K$,the standard enthalpy and standard entropy changes are $-382.64 \ kJ \ mol^{-1}$ and $-145.6 \ J \ K^{-1} \ mol^{-1}$ respectively. The standard Gibbs energy change for the same reaction at $298 \ K$ is $..... \ kJ \ mol^{-1}$.

For a spontaneous change,free energy change $\Delta G$ is