The heat of reaction can be determined experimentally using a device called a

1. Analyze the question The question asks which device is used to determine the heat of reaction experimentally. The heat of reaction is the amount of heat absorbed or released during a chemical reaction (the enthalpy change, ΔH).

2. Explain the concept To measure heat changes, we use calorimetry. A calorimeter is an insulated container in which a reaction takes place. The heat released or absorbed changes the temperature of a known mass of water (or solution) around the reaction. We then calculate the heat using:

q = mcΔT

where:

• q = heat energy (joules)
• m = mass of the water or solution (g)
• c = specific heat capacity (for water, 4.2 J g⁻¹ K⁻¹)
• ΔT = change in temperature (K or °C)

3. Go through the options

• A. Calorimeter: Designed to measure heat changes in reactions. ✔
• B. Barometer: Measures atmospheric pressure. ✘
• C. Spectrometer: Measures the spectrum of light or radiation, used to analyze composition. ✘
• D. Thermometer: Measures temperature only. It is used inside a calorimeter to record ΔT, but it does not measure the heat of reaction by itself. ✘

4. Answer The device used to determine the heat of reaction is a calorimeter, which is option A.

5. Exam tip Remember the word root: calor means heat, so a calorimeter measures heat. Be careful with option D: a thermometer measures temperature, which is not the same thing as heat. Exam setters often use that distinction to catch students.