Open Question
Which evaporates more quickly: 55 mL of water in a beaker with a diameter of 4.5 cm or 55 mL of water in a dish with a diameter of 12 cm, and is the vapor pressure of the water different in the two containers? Explain.
Ch.11 - Liquids, Solids & Intermolecular Forces
Chapter 11, Problem 56
Why is the heat of vaporization of water greater at room temperature than at its boiling point?
Verified step by step guidance1
Understand that the heat of vaporization is the energy required to convert a liquid into a gas at constant temperature and pressure.
Recognize that at the boiling point, the liquid and gas phases are in equilibrium, meaning the molecules have enough energy to overcome intermolecular forces.
At room temperature, water molecules have less kinetic energy compared to the boiling point, so more energy is needed to overcome the intermolecular forces to vaporize.
Consider that the heat of vaporization is higher at room temperature because the energy difference between the liquid and gas phases is greater than at the boiling point.
Conclude that the additional energy required at room temperature is due to the need to increase the kinetic energy of the molecules to reach the energy level at which they can vaporize.
Related Practice
Textbook Question
Which evaporates more quickly: 55 mL of water (H2O) in a beaker or 100 mL of acetone [(CH3)2CO] in an identical beaker under identical conditions? Is the vapor pressure of the two substances different? Explain.
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Open Question
Why does spilling room-temperature water over your skin on a hot day cool you down while spilling room-temperature vegetable oil does not?
Open Question
The human body obtains 915 kJ of energy from a candy bar. If this energy were used to vaporize water at 100.0 °C, how much water (in liters) could be vaporized? (Assume the density of water is 1.00 g/mL.)
Open Question
A 100.0-mL sample of water is heated to its boiling point. How much heat (in kJ) is required to vaporize it? (Assume a density of 1.00 g/mL.)
Textbook Question
Suppose that 0.95 g of water condenses on a 75.0-g block of iron that is initially at 22 °C. If the heat released during condensation goes only to warming the iron block, what is the final temperature (in °C) of the iron block? (Assume a constant enthalpy of vaporization for water of 44.0 kJ/mol.)
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