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MCAT Chemistry Question — Vaporization

All of the following are true regarding the vaporization of water EXCEPT:

  1. the velocity of the gas molecules increase
  2. the system’s entropy increases
  3. the products have more kinetic energy
  4. the intramolecular forces of water are broken




This question tests your understanding of the physical properties involved in the conversion of water from liquid to gas, as follows.


H2O (l) + heat →H2O (g)

As a general rule, molecules in the gas phase always have more kinetic energy than their liquid counterparts. Since KE is proportional to the square of velocity, it follows that the gas molecules also increase in velocity, eliminating A and C. As shown in the equation above, the vaporization of water is an endothermic process, making B a true statement. When liquid is converted to gas, intermolecular bonds are broken but intramolecular bonds remain in tact making D the correct answer.


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