# Physical meaning of $SdT$

Consider a thermodynamic classical closed system. Due to the First and Second laws of thermodynamics, we know that $$dU=\delta Q-\delta W=TdS-PdV$$, and we could assign to $$\delta Q=TdS$$ the meaning of exchanged heat.

But what physical meaning could we assign to $$SdT$$ appearing, e.g., in the expression for a reversible Helmholtz free energy variation, $$dA=-SdT-PdV$$?

Consider the constant V case (say, you have a fixed size container of a gas): The $$dA$$ then is given by $$dA = -SdT$$ Thus $$SdT$$ : For a fixed volume container, how much free energy will decrease by increasing the temparature of the system.