Endothermic versus Exothermic Reactions

What is an endothermic reaction?

• A) A reaction that only occurs in living organisms

• B) A reaction that does not involve heat exchange

• C) A reaction that releases heat to the surroundings

• D) A reaction that absorbs heat from the surroundings

Answer explanation

An endothermic reaction is characterized by the absorption of heat from the surroundings, making option D the correct choice. This contrasts with exothermic reactions, which release heat.

Which statement is true about endothermic reactions?

• They absorb energy from the surroundings

• They are always faster than exothermic reactions

• They occur only in chemical laboratories

• They release energy in the form of light

Answer explanation

Endothermic reactions are characterized by their ability to absorb energy from the surroundings, which distinguishes them from exothermic reactions that release energy. Thus, the correct statement is that they absorb energy.

Which of the following is an example of an exothermic reaction?

• Melting ice

• Evaporation of water

• Combustion of gasoline

• Photosynthesis

Answer explanation

The combustion of gasoline is an exothermic reaction because it releases energy in the form of heat and light. In contrast, melting ice and evaporation of water are endothermic processes, while photosynthesis absorbs energy.

What happens to the energy in an exothermic reaction?

• A) Energy is converted into mass

• B) Energy remains constant

• C) Energy is absorbed from the surroundings

• D) Energy is released to the surroundings

Answer explanation

In an exothermic reaction, energy is released to the surroundings as heat. This is why option D is correct, as the reaction results in a net loss of energy from the system to the environment.

How does an exothermic reaction affect the temperature of its surroundings?

• It increases the temperature

• It has no effect on the temperature

• It stabilizes the temperature

• It decreases the temperature

Answer explanation

An exothermic reaction releases energy in the form of heat, which increases the temperature of its surroundings. Therefore, the correct answer is that it increases the temperature.