The first law of thermodynamics is not adequate in predicting the direction of a process. it is the law of conservation of energy. However it does not predict whether the process will occur spontaneously and if so, in which direction. For example, the first law of thermodynamics does not indicate whether heat can flow from colder end to a hotter end or not. All that the first law tells is that if the process occurs, the heat energy gained by one end would be exactly equal to that lost by the other end. To predict the direction of process, entropy and free energy change values should be used instead.