Name: Third Law of Thermodynamics
Uploaded: 2019-07-19
Duration: 3 min 41 s
Description: The third law of thermodynamics was developed by a chemist, Walther Nernst, and is therefore often referred to as Nernst's theorem or Nernst's postulate. Lea...

Question

Write short note on heat of reaction.

Accepted Answer

Heat of reaction, the amount of heat that must be added or removed during a chemical reaction in order to keep all of the substances present at the same temperature. Thus, the heat of reaction determined at constant pressure is also designated the enthalpy of reaction, represented by the symbol $ΔH$ . If the heat of reaction is positive, the reaction is said to be endothermic, whereas if heat of reaction is negative, the reaction is said to be exothermic.

Measurement of heat change at constant pressure (generally under atmospheric pressure) can be done in a calorimeter shown in figure. We know that $∆ Η = q_{p}$ (at constant p) and, therefore, heat absorbed or evolved, $q_{p}$ at constant pressure is also called the heat of reaction or enthalpy of reaction, $∆_{r} H$ . In an exothermic reaction, heat is evolved, and system loses heat to the surroundings. Therefore, $q_{p}$ will be negative and $∆_{r} H$ will also be negative. Similarly, in an endothermic reaction, heat is absorbed, $q_{p}$ is positive and $∆_{r} H$ will be positive.

Write short note on heat of reaction.

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