State the First Law of Thermodynamics and its significance in chemical engineering.

The First Law states that energy cannot be created or destroyed, only converted from one form to another: dU = dQ - dW, where dU is internal energy change, dQ is heat added, and dW is work done by the system. For chemical engineering, it is the basis for energy balances around processes, sizing heat exchangers, calculating heating/cooling requirements, and analyzing power cycles. For open systems: dH = dQ - dWs (shaft work), making enthalpy the key property.