Why is it important to know the temperature of both reactants and products of a reaction in order to determine change in the Gibbs free energy of the reaction?
Is it because temperature has an effect on both enthalpy and entropy? Or is it because of some other reason I am missing?
Any help on this would be great. Thanks!
Answer
Change in the Gibbs free energy ($\Delta$$\ce{G}$) of a reaction at any temperature can be determined by the equation <$$\ce{$\Delta$G = $\Delta$G^0 + RTlnQ_c (Q_p if the reactants and products are gaseous)}$$ Here, $\Delta$$\ce{G^0}$ is the standard Gibbs-free energy change of the reaction which is determined by,$$\ce{$\Delta$G^0 = $\Sigma$a_iG^0_i_{products} - $\Sigma$b_iG^0_i_{reactants}}$$ where $\ce{a_i}$s and $\ce{b_i}$s are proper stoichiometric coefficients. Now, $\ce{G^0}$ of products or reactants are determined by producing 1 mole of ech of them from their corresponding constituting elements in their standard states and at a FIXED TEMPERATURE(generally at $\ce{298.15K}$). So, $\ce{$\Delta$G^0}$ is determined also at that particular temperature,So, it is independent of Temperature.
But,when we have to calculate $\ce{$\Delta$G}$ for any reaction at any temperature($T$) by the above given relationship , we have to know the temperature of the reaction condition as you can see clearly, $\ce{$\Delta$G}$ is directly dependent on $\ce T$.
That's why, it's important to know the temperature.
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