Exothermic process

Welcome to our episode on the chemistry of warmth! We will explore the fascinating world of exothermic processes, the direct opposite of the endothermic reactions we discussed previously. An exothermic process is any chemical reaction or physical change that releases energy, usually as heat, causing its surroundings to warm up. From the comforting crackle of a bonfire to the instant heat of a chemical hand-warmer, we will delve into the molecular reasons for this energy release. You'll learn why the enthalpy change for these processes is negative, how we measure the heat using calorimetry, and what it takes to get these energy-releasing reactions started.

Check your understanding

These are the same multiple-choice questions you will see in the Quiz section after you listen to the episode. Use them here to preview or review the answers.

What is the defining characteristic of an exothermic process?

  1. It absorbs energy from the surroundings.
  2. It requires a constant input of light to proceed.
  3. It releases energy from the system into the surroundings.
  4. The temperature of the system increases.
  5. It only occurs at very high pressures.

What is the sign of the change in enthalpy (ΔH) for an exothermic reaction and what does it signify?

  1. Positive, because the system has gained energy.
  2. Negative, because the system has lost energy to the surroundings.
  3. Zero, because energy is conserved in the reaction.
  4. Positive, because the products have more energy than the reactants.
  5. Negative, because the reaction absorbs heat.

From where does the energy released during an exothermic chemical reaction primarily originate?

  1. From the kinetic energy of the reacting molecules.
  2. From the external environment.
  3. From the conversion of mass into energy.
  4. From the formation of new chemical bonds in the products that are stronger and more stable than the bonds in the reactants.
  5. From the release of electrons to the surroundings.

Why do many spontaneous exothermic reactions, such as burning wood, require an initial input of energy like a match?

  1. To increase the concentration of the reactants.
  2. To overcome the activation energy barrier needed to start the reaction.
  3. To decrease the entropy of the system.
  4. To convert the reactants from solid to gas.
  5. To make the ΔG of the reaction negative.

Which of the following are examples of exothermic processes? (Select all that apply)

  1. Burning a candle
  2. Melting ice cubes
  3. The condensation of steam into liquid water
  4. A chemical hand-warmer getting hot
  5. Photosynthesis in a plant leaf

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