Question

You and a friend are studying for a chemistry exam. What if your friend says "Exothermic processes are favored and the sign of the enthalpy change tells whether or not a process is endothermic or exothermic. Therefore, the sign of ${\mathbf{\Delta H}}_{\mathbf{\text{soln}}}$tells us whether or not a solution will form". How would you explain to your friend that this conclusion is not correct? What part, if any, of what your friend says is correct.

Short answer

Gibbs’s free energy of solution determines the formation of solution.

My friend is correct in the part that the sign of enthalpy determines whether the reaction is endothermic or exothermic.

Step-by-step solution

Gibbs free energy equation:

$\mathrm{\Delta }\text{G}=\mathrm{\Delta }\text{H}-\text{T}\mathrm{\Delta }\text{S}$

$\mathrm{\Delta }\text{G}\text{=}$change in Gibbs Free Energy

$\mathrm{\Delta }\text{H}\text{=}$change in enthalpy

T = temperature in Kelvin

$\mathrm{\Delta S}=$change in entropy

 Sign of ΔH

Negative sign of $\mathrm{\Delta }{\text{H}}_{\text{soln}}$indicates exothermic reaction by convention

Positive sign of $\mathrm{\Delta }{\text{H}}_{\text{soln}}$ indicates endothermic reaction by convention