In this lesson our instructor talks about energy and chemical reactions. First, he talks about the first law of thermodynamics, calculating ∆U, Q, and W, and constant-volume calorimetry. Then he discusses constant-pressure conditions, calculating enthalpy, phase changes, heats of reaction, and using standard enthalpies of formation. He also lectures on enthalpy from a series of reactions and coffee-cup calorimetry. Energy & Chemical Reactions State functions are path-independent. The first law of thermodynamics states that energy is conserved during a chemical reaction. Energy can be transferred through heat and work. Calorimetry problems involve either constant-volume or constant-pressure scenarios. Enthalpy is the amount of heat transferred under constant pressure.