![]() There must be a chemical potential – a concept introduced by J. Then a fraction of this energy is converted into vibrations and sound waves, while another portion is used to overcome the cohesive energy of the ceramic as the mug strikes the floor. ![]() Gravitational potential energy is converted into translational energy as the system accelerates toward the floor. The system (ceramic plus finely brewed dark roasted aqueous extract of Arabica beans) spontaneously falls to the ground to lower its energy. Raise a coffee mug one meter off the ground. We have an instinctive feeling that systems tend to lower their energy. We quantify the changes in U and H by measuring temperature changes at either constant volume or constant pressure. The temperature increases when an exothermic reaction occurs in a thermos flask and decreases during the course of an endothermic reaction. Certainly, temperature changes upon mixing and subsequent reaction are indicative of chemical changes. From the Zeroth and First Laws of Thermodynamics we have defined a state variable (temperature T) and two state functions (internal energy U and enthalpy H) that we know exist and are rather fundamental. Not much chemistry is performed without making products. When two chemicals are mixed together do they react? This is an existential question for a synthetic chemist.
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