CLEP Chemistry Practice Test

Category - Chemistry

Which of the following statements best describes what happens to water during evaporation?
  1. The temperature of the water increases until the water molecules react with nitrogen in the air.
  2. Water molecules on the surface overcome intermolecular forces and change into the gas phase.
  3. Water molecules on the surface come in contact with air molecules and are pulled into the gas phase.
  4. The temperature of the water increases until the water molecules separate and form oxygen and hydrogen gas.
Explanation

Answer: B - The statement that best describes what happens to water during evaporation is "Water molecules on the surface overcome intermolecular forces and change into the gas phase."

Evaporation is a process where a liquid changes into a gas. This happens when the temperature of the liquid increases or when the pressure of the gas above the liquid decreases. In the case of water, evaporation occurs when the water molecules on the surface of the liquid overcome the intermolecular forces that hold them together and change into the gas phase.

Water molecules are held together by hydrogen bonds, which are strong intermolecular forces that require a significant amount of energy to break. As the temperature of the water increases, the kinetic energy of the water molecules also increases. This means that the molecules move faster and collide with each other more frequently. When a water molecule at the surface of the liquid gains enough kinetic energy, it can break free from the hydrogen bonds and enter the gas phase.

Once in the gas phase, the water molecules continue to move and collide with each other, but they are now free to move throughout the space they occupy. The water molecules in the gas phase are also more spread out than in the liquid phase, which means they have a higher entropy (disorder). The energy required to convert water from the liquid phase to the gas phase is called the heat of vaporization and is a measure of the energy required to break the intermolecular forces holding the liquid together.

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