Humber Admissions Practice Test

Which of the following statements about combustion reactions is true?

1. They can occur without oxygen.

2. They only occur with liquid fuels.

3. They release energy in the form of heat and light.

4. They do not produce any gases.

The correct answer is: They release energy in the form of heat and light.

Combustion reactions are chemical processes that involve the rapid combination of a fuel with oxygen, resulting in the production of heat and often light. The key characteristic of combustion is the release of energy; this energy manifests primarily as thermal energy (heat) and can also produce visible light, particularly in the case of flames. In essence, the energy released during combustion is a result of the breaking and forming of chemical bonds, which releases more energy than is consumed in the reaction. This is why the statement regarding energy release in the form of heat and light is indeed true. The other statements do not accurately describe combustion reactions. For instance, combustion typically requires an oxidizing agent like oxygen, and while it can involve different states of matter for the fuel (not exclusively liquid), the process is not limited to any particular state. Additionally, combustion reactions often produce gases, such as carbon dioxide and water vapor, as byproducts, making the statement about not producing any gases incorrect.