Thermodynamics describes heat, work, and energy transfer in systems. The first law of thermodynamics states that energy is conserved, with internal energy changes equaling heat transferred plus work done. The second law states that entropy increases over time as energy distributed more evenly, limiting conversion of heat to work to less than 100% efficiency. Thermodynamic processes include isothermal (constant temperature), adiabatic (no heat transfer), isovolumetric (no volume change), and cyclic (returning to initial conditions). Heat engines use heat to do work but also dissipate heat, with efficiency measured as useful work over heat input. The predicted "heat death" of the universe occurs when entropy reaches its maximum and temperature is uniform