Concept:The heat of reaction is measured experimentally as heat absorbed or released during a reaction.
Explanation:A calorimeter is the device used to measure the heat of reaction.
It insulates the reaction vessel to reduce heat exchange with the surroundings.
The temperature change of the reaction mixture is then observed.
From this change, the heat evolved or absorbed is calculated using
q=mcΔT.
A barometer measures atmospheric pressure.
A spectrometer analyses light spectra.
A thermometer only measures temperature, not heat change directly.
Answer:A. Calorimeter