The conservation of energy
Start with the big picture
The First Law states that energy is conserved: it can be transferred as heat or work, but it is not created or destroyed. In chemistry, the relationship is written ΔU = q + w, with heat and work positive when energy enters the system and negative when it leaves. Internal energy is a state function, whereas heat and work depend on the process. These ideas clarify energy changes in isolated, adiabatic, isothermal, and cyclic processes. The lesson also connects internal energy to enthalpy and heat capacities, introduces PV-work and other forms of work, and explains why a perpetual motion machine of the first kind is impossible. Together, these concepts provide a framework for accounting for energy in thermodynamic systems.
What you'll learn
- State the First Law and express it using internal energy, heat, and work.
- Apply the chemistry sign convention to heat and work transfers.
- Distinguish the state function internal energy from path functions heat and work.
- Describe energy relationships in isolated, adiabatic, isothermal, and cyclic processes.
- Relate enthalpy and heat capacities to energy accounting.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
