4. Most chemical reactions what we discuss in chemistry occur on the lab bench and are therefore open systems at constant pressure. Under these conditions we can observe and measure the heat exchange between the system and surroundings. This heat exchange for a reaction is called change in enthalpy, AH. Consider the following systems and discuss whether they are endothermic (system absorbs heat from the surroundings) or exothermic (system releases heat to the surroundings). Add energy to the equation as a reactant or product for each and think about what the sign for AH is for each. H2O(1) → H2O(s) H2O(s) → H2O(1) H2O(1) → H2O(g)
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
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