Not all of the heat energy taken from the source is being used to performed useful work. Some fraction of the heat energy must always be rejected, at a temperature cooler than that of the warm source to the environment The second law of thermodynamics Kelvin statement It is impossible to convert heat completely into works in a cyclic process. Clausius statement Heat generally cannot flow spontaneously from a material at lower temperature to a material at higher temperature In a system a process that occurs will tend to increase the total entropy of the universe work done Efficiency <100% energy put into the systemNot all of the heat energy taken from the source is being used to performed useful work. Some fraction of the heat energy must always be rejected, at a temperature cooler than that of the warm source, to the environment. – The second law of thermodynamics Kelvin statement: It is impossible to convert heat completely into works in a cyclic process. Clausius statement: Heat generally cannot flow spontaneously from a material at lower temperature to a material at higher temperature. In a system, a process that occurs will tend to increase the total entropy of the universe. Efficiency = work done energy put into the system < 100%