They can measure the spontaneity of the reaction with the form, Substituting the values of in the above expression information mostly on the playfulness of the reaction would be given to us from the expression above. This reaction is spontaneous if the price of is negative, and if it is positive the response is not random. At equilibrium, the values of are 0.
It decreases because nuclear charge increases across a row, electrons are added to the same shell and shielding remains constant. Therefore the outer electrons are more attracted to the nucleus making the atom smaller.