International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What does the symbol ΔH represent?

1. Change in temperature

2. Change in pressure

3. Energy change

4. Change in volume

The correct answer is: Energy change

The symbol ΔH represents the change in enthalpy, which is a measure of the total heat content of a system at constant pressure. When a reaction occurs, the ΔH value indicates whether the reaction releases heat (exothermic) or absorbs heat (endothermic). This is integral in thermodynamics and helps in understanding energy changes associated with chemical reactions. In contrast, the other symbols refer to different thermodynamic changes. Change in temperature pertains to how the temperature of a substance changes, which is not directly what ΔH indicates. Change in pressure relates to the force exerted by gases in a system but does not encapsulate the concept of heat exchange as ΔH does. Change in volume signifies alterations in the space a substance occupies, which is also not the focus of ΔH. Each of these terms has its own specific implications in physics and chemistry but does not define the heat exchange characteristic of ΔH.