Freezing is an exothermic process because it releases heat energy to the surroundings. 1 When a substance transitions from a liquid to a solid state, the particles lose kinetic energy, come closer together, and form stronger intermolecular forces, releasing heat in the process.
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Key Takeaways: Is Freezing Endothermic or Exothermic?
- Freezing is an exothermic process as it releases heat energy to the surroundings during the transition from a liquid to a solid state.
- As a substance cools, its molecules lose kinetic energy and form stronger intermolecular forces, leading to the release of excess energy as heat.
- Freezing is not endothermic because it does not absorb heat energy from the surroundings but rather releases it, distinguishing it from endothermic processes.
Why is freezing an exothermic process?
Freezing is an exothermic process because it involves the release of heat energy. 2 When a substance undergoes freezing, its molecules lose energy and slow down, leading to the formation of a solid state. During this transition, the excess energy is released into the surroundings as heat. 3
Freezing occurs when a substance transitions from a liquid to a solid state due to a decrease in temperature. At higher temperatures, the molecules in the liquid have more kinetic energy and move more freely.
As the temperature drops, the average kinetic energy of the molecules decreases. 4 5 At the freezing point, the molecules have lost enough energy to form stable bonds and arrange themselves into a solid structure.
This process of molecular rearrangement releases excess energy, which is transferred to the surrounding environment as heat.
The release of heat energy during freezing can be observed in everyday life. For example, when water freezes, the surrounding air or the surface it is in contact with may feel warmer due to the energy being released.
Similarly, the formation of ice in a freezer leads to the extraction of heat from the food items stored inside, helping to preserve them at lower temperatures.
Overall, freezing is an exothermic process because it involves the release of energy as heat when a substance transitions from a liquid to a solid state.
Why is freezing not an endothermic process?
Freezing is not an endothermic process because it does not absorb heat energy from the surroundings. Instead, it releases heat energy during the transition from a liquid to a solid state. This release of energy is what makes freezing an exothermic process.
During freezing, the molecules in a substance lose energy and slow down, resulting in the formation of a solid. This process involves the conversion of the substance’s latent heat of fusion into sensible heat, which is released as thermal energy.
The latent heat of fusion is the energy required to break the intermolecular forces holding the molecules together in the liquid state and convert them into a solid state. 6
As the substance cools and reaches its freezing point, the molecular motion decreases, and the molecules come together to form a more organized arrangement characteristic of a solid.
This release of energy helps maintain thermal equilibrium and is why freezing is considered an exothermic process.
Unlike endothermic processes that absorb heat from the surroundings, freezing actively releases heat energy, making it exothermic in nature.
Further reading
Is Evaporation Endothermic or Exothermic?
Is Condensation Endothermic or Exothermic?
Is Deposition Endothermic or Exothermic?
Is Boiling Endothermic or Exothermic?
Is Photosynthesis Endothermic or Exothermic?
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References
- 11.4: Phase Changes. (2014, November 18). Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Chemistry_-_The_Central_Science_(Brown_et_al.)/11%3A_Liquids_and_Intermolecular_Forces/11.04%3A_Phase_Changes
- Freezing – Wikipedia. (2022, November 3). Freezing – Wikipedia. https://en.wikipedia.org/wiki/Freezing
- 9.5: Endothermic and Exothermic Reactions. (2021, April 16). Chemistry LibreTexts. https://chem.libretexts.org/Courses/Portland_Community_College/CH104%3A_Allied_Health_Chemistry_I/09%3A_Energy_and_Chemical_Reactions/9.05%3A_Endothermic_and_Exothermic_Reactions
- Study.com https://homework.study.com/explanation/what-happens-to-the-average-kinetic-energy-of-the-molecules-of-a-warm-substance-when-the-temperature-of-the-substance-is-slightly-decreased-a-it-increases-b-it-decreases-c-it-becomes-zero-d-it-remains-unchanged.html
- 13.5: Average Kinetic Energy and Temperature. (2016, June 27). Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Introductory_Chemistry_(CK-12)/13%3A_States_of_Matter/13.05%3A_Average_Kinetic_Energy_and_Temperature
- 11.3 Phase Change and Latent Heat – Physics | OpenStax. (n.d.). 11.3 Phase Change and Latent Heat – Physics | OpenStax. https://openstax.org/books/physics/pages/11-3-phase-change-and-latent-heat