Explain how heat absorbed at constant pressure is measured using coffee calorimeter with neat diagram.

Explanation

(i) Measurement of heat change at constant pressure can be done in a coffee cup calorimeter .
(ii)We know that `DeltaH=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, `DeltaH_r`.
(iii) In an exothermic reaction, heat is evolved, and system loses heat to the surroundings Therefore `q_P` will be negative and `DeltaH_r` will also be negative.
(iv) Similarly in an endothermic reaction, heat is absorbed `q_P` is positive and `DeltaH_r` will also be positive.