A Gibbs-Duhem relationship in economics, Slutsky conditions, and the relationship proposed by marginalist theory between exchange value and value in use was found from a phenomenological description and tested considering the macroeconomic equations. To simplify the calculations, it was considered that the economic systems are in equilibrium to make an analogy with the thermodynamics of equilibrium. In addition, fundamental considerations were made, such as considering that a consumer's wealth or a small country is constant for the existence of a measurable (quantifiable) utility function. However, according to the discussion, it could be seen that W. Saslow's theory must be developed in the field of non-equilibrium thermodynamics, which is why the economy is not a system that is in equilibrium, but rather, on the contrary, the economy is a dynamic system.