Question

From my understanding, an exothermic reaction has a negative change in enthalpy meaning that energy is released to the surroundings. However, is it correct to say that during this exothermic process, the enthalpy change of the surroundings is positive? Does this mean that whenever a system has a negative change in enthalpy, another system must have a positive change in enthalpy?

Also, I was wondering what the distinction between change in enthalpy and change in heat energy is. I was told that the change in heat energy has an opposite sign to that of enthalpy during a process. Hence, does heat energy refer to the surroundings??

Answer 1

In an exothermic reaction, the system's change in enthalpy is negative, indicating energy release, which results in a positive change in enthalpy for the surroundings. The heat energy 'q' has an opposite sign to that of the system's change in enthalpy since it is from the perspective of the surroundings.

Step-by-step explanation:

When a chemical reaction occurs, we often refer to either an exothermic or endothermic process in terms of heat exchange. In an exothermic process, where the change in enthalpy (ΔH) of the system is negative due to the release of energy, the surrounding environment indeed experiences a positive change in enthalpy because it absorbs the energy released by the system. This means that energy is seen as a product of the reaction.

The change in heat energy, represented by 'q', has a sign convention that is opposite to that of enthalpy for the system during a process. Therefore, for an exothermic reaction, 'q' is negative for the system because it is losing heat, but 'q' would be considered positive for the surroundings which are gaining heat. The heat energy, in this case, indeed refers to the energy exchange with the surroundings.