How would you find out whether a reaction is feasible?

For a reaction to be feasible at a given temperature, it must happen spontaneously, which means no extra energy needs to be put in for the reaction to occur. To find out whether a reaction is feasible, you can calculate the Gibbs free energy change (ΔG) for that particular reaction. ΔG = ΔH - TΔSΔH is the enthalpy change for the reaction (which you can calculate from a Hess cycle), T is the temperature at which the reaction is occurring, and ΔS is the entropy change associated with the reaction. You can find this by subtracting the sum of the standard entropies of the reactants from the sum of the standard entropies of the products, all of which can be found in a data book. A reaction only occurs spontaneously if the Gibbs free energy change is less than zero (ie ΔG is negative). This means that exothermic reactions (negative ΔH) which result in an increase in entropy (positive ΔS) will always be feasible at any temperature, and reactions that are endothermic (positive ΔH) and cause a decrease in entropy (negative ΔS) are never feasible, since ΔG would be positive.