Label each of the following reactions as exothermic or endothermic ("exo" or "endo"), and according to whether work is done on or by the system, or no work is done at all ("on", "by" or "none")? Note that no "endo-on" cases appear here, as these are always thermodynamically unfavourable. There is no need to do any calculation, use chemical arguments to predict the sign of the enthalpy change. Options: exo-on, exo-by, endo-by, exo-none NH3(g) + HCl(g) --> NH 4 Cl(s) Cl2(aq) + 2 KBr(aq) --> 2 KCl(aq)+Br 2 (aq) N2 (l)--> N2 (g) S(s)+3/2 O 2 (g) --> SO3 (g) Zn(s) + 2HCl(aq) --> ZnCl 2 (aq)+H 2 (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.
Label each of the following reactions as exothermic or endothermic ("exo" or "endo"), and according to whether work is done on or by the system, or no work is done at all ("on", "by" or "none")? Note that no "endo-on" cases appear here, as these are always
NH3(g) + HCl(g) --> NH 4 Cl(s)
Cl2(aq) + 2 KBr(aq) --> 2 KCl(aq)+Br 2 (aq)
N2 (l)--> N2 (g)
S(s)+3/2 O 2 (g) --> SO3 (g)
Zn(s) + 2HCl(aq) --> ZnCl 2 (aq)+H 2 (g)
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