Energy is used all around us and is involved in many chemical processes. An energy balance is used to keep track of the energy used in each part of the system. An engineers job is to manage the required energy and find a way to reduce the energy requirement. Two types of systems that engineers deal with are adiabatic and isothermal. An adiabatic process is one in which there is no change in the temperature of the system. Whereas an isothermal system is when no phase changes or chemical reactions take place. Energy always follows the first law of thermodynamics which states that energy can neither be created or destroyed only conserved. It is impossible to know the exact values of internal energy (U) or enthalpy (H) only the change in theses values. A reference state, mostly 0 or 25 degrees Celsius is used so that values of U and H can be used in problems. One equation used in some energy balance equations is the change in enthalpy plus the change in kinetic and potential energy equals the energy transferred. A problem involving energy balances involves steam tables and using tables of enthalpy found in the back of the textbook.