What instrument is used to measure the heat involved in a chemical reaction or process?

• A. Hess's Law
• B. Calorimeter
• C. Photosynthesis
• D. Bond energy

Answer: (B)

Measuring heat changes in a chemical reaction is done with a calorimeter. A calorimeter is designed to isolate the reaction so that the heat it releases or absorbs appears as a measurable change in temperature. In a simple setup like a coffee cup calorimeter, the reaction is carried out in an insulated vessel and the heat exchanged with the surroundings is calculated from the temperature rise of the solution, using q = m c ΔT (with the calorimeter’s own heat capacity accounted for). For reactions where the energy is released by burning fuel, a bomb calorimeter is used; it runs the reaction at constant volume and converts the temperature change of the calorimeter into the heat released, based on the calorimeter’s total heat capacity. The essential idea is that the instrument translates the invisible heat flow into a readable temperature change, allowing you to quantify the enthalpy change of the process.

Other terms here aren’t instruments: Hess’s Law is a method to calculate heat changes by combining known enthalpies; photosynthesis is a biological process that stores energy from light; bond energy is a concept describing the energy required to break bonds, not something that measures heat itself.