What is the key difference between endothermic and exothermic reactions?

• A. Endothermic reactions release energy while exothermic absorb energy
• B. Exothermic reactions do not involve energy changes
• C. Endothermic reactions absorb energy from surroundings
• D. Exothermic reactions absorb energy from surroundings

Answer: (C)

The key difference between endothermic and exothermic reactions lies in how they interact with energy. In endothermic reactions, energy is absorbed from the surroundings, often in the form of heat, resulting in a decrease in the temperature of the surrounding environment. This is why we observe that these types of reactions often require an external source of energy to proceed.

For example, in photosynthesis, plants absorb sunlight to convert carbon dioxide and water into glucose and oxygen, illustrating an endothermic process where energy input is necessary.

In contrast, exothermic reactions release energy into the surroundings, typically in the form of heat, leading to an increase in the temperature of the surrounding environment. Combustion reactions, such as burning wood or fossil fuels, are classic examples of exothermic reactions where energy is released.

The other choices present misunderstandings about these energy dynamics, with one incorrectly stating that endothermic reactions release energy, while another claims that exothermic reactions do not involve energy changes at all.