Melting ice is an endothermic process. It requires the absorption of energy in the form of heat to break the hydrogen bonds holding the water molecules together. 1 This energy is taken from the surrounding environment, resulting in a decrease in temperature.
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Key Takeaways: Is Melting Ice Endothermic or Exothermic?
- Melting ice is an endothermic process because it requires the absorption of heat energy to break the intermolecular forces holding the ice together.
- The heat energy is used to overcome these forces and convert the solid ice into liquid water.
- The absorbed heat energy is utilized in breaking the bonds between water molecules, rather than increasing the temperature of the substance.
Why is melting ice an endothermic process?
Melting ice is an endothermic process because it requires the absorption of heat energy from the surroundings in order to overcome the forces of attraction between the water molecules and break the solid lattice structure of ice.
In a solid, such as ice, the water molecules are arranged in a regular, ordered pattern held together by intermolecular forces. 2 These forces of attraction between the water molecules in ice are relatively strong, keeping the molecules in a fixed position and maintaining the solid state.
When heat is applied to ice, the energy is absorbed by the water molecules. This increased energy causes the molecules to vibrate more vigorously, weakening the intermolecular forces that hold the solid structure together. As a result, the ice begins to melt and transitions into the liquid state.
The heat energy absorbed during this process is used to overcome the intermolecular forces, rather than increasing the kinetic energy or temperature of the substance.
This is why the temperature remains constant during the phase change from solid to liquid, even though heat is being added. The absorbed heat energy is utilized in breaking the bonds between the water molecules and converting the solid ice into liquid water. 3
Since the melting process requires an input of heat energy from the surroundings, it is considered an endothermic process. The term “endothermic” means “absorbing heat,” and melting ice is an example of such a process.
Why is melting ice not an exothermic process?
Melting ice is not an exothermic process because it does not release heat energy into the surroundings. Instead, it requires an input of heat energy from the surroundings to overcome the forces holding the ice together and transition it into a liquid state.
When ice melts, it undergoes a phase change from a solid to a liquid. During this process, the energy supplied to the ice is used to break the intermolecular forces that hold the solid lattice together.
The energy is absorbed by the ice as latent heat, which is necessary for the transition to occur. 4 5 As a result, the surroundings do not receive any excess heat energy, and the process is considered endothermic.
In an exothermic process, energy is released into the surroundings. This occurs when a substance undergoes a phase change in the opposite direction, such as when water vapor condenses to form liquid water or when liquid water freezes to form ice.
In both of these cases, the energy is released to the surroundings as heat. However, during the melting of ice, heat energy is required, not released, making it an endothermic process.
Further reading
Is Sublimation Endothermic or Exothermic?
Is Melting Endothermic or Exothermic?
Is Freezing Exothermic or Endothermic?
Is Melting Point a Physical or Chemical Property?
Is Luster a Physical or Chemical Property?
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References
- Melting – CHEMISTRY COMMUNITY. (n.d.). Melting – CHEMISTRY COMMUNITY. https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=89431
- O. (n.d.). The Solid State of Matter – Chemistry. The Solid State of Matter – Chemistry. https://pressbooks-dev.oer.hawaii.edu/chemistry/chapter/the-solid-state-of-matter/
- Phase Change and Latent Heat | Physics. (n.d.). Phase Change and Latent Heat | Physics. https://courses.lumenlearning.com/suny-physics/chapter/14-3-phase-change-and-latent-heat/
- ESA – Eduspace EN – Global Change – Ice – a special substance. (n.d.). ESA – Eduspace EN – Global Change – Ice – a Special Substance. https://www.esa.int/SPECIALS/Eduspace_Global_EN/SEMHE7TWLUG_0.html
- ATMO336 – Fall 2018. (n.d.). ATMO336 – Fall 2018. http://www.atmo.arizona.edu/students/courselinks/fall16/atmo336s2/lectures/sec1/water.html