In an exothermic reaction, heat flows in.
True
False
The correct answer and explanation is:
Correct Answer: False
In an exothermic reaction, heat does not flow in; instead, it flows out of the system into the surroundings. This is the defining feature of exothermic reactions—they release energy, usually in the form of heat, as the reaction proceeds. The term “exothermic” comes from the Greek words exo meaning “outside” and thermic meaning “heat.” Therefore, exothermic literally means “heat out.”
During an exothermic reaction, the total energy of the products is lower than that of the reactants. This is because the bonds formed in the products release more energy than the energy required to break the bonds in the reactants. The excess energy is released as heat, which is why such reactions often feel warm or even hot to the touch. A good example of an exothermic reaction is combustion. When substances like wood or gasoline burn, they release heat and light energy.
Another example is the reaction between water and calcium chloride. When calcium chloride dissolves in water, the temperature of the solution increases due to the release of heat.
In contrast, endothermic reactions absorb heat from the surroundings. This means that in those reactions, heat flows in, causing the surrounding environment to feel cooler. An example of an endothermic reaction is the process of photosynthesis or the dissolving of ammonium nitrate in water, which causes the solution to become cold.
To summarize, in an exothermic reaction, heat flows out, not in. Saying that “heat flows in” during an exothermic reaction is incorrect and actually describes the opposite type of reaction—endothermic. Understanding the direction of heat flow is essential for correctly identifying and classifying chemical reactions based on their energy changes.