Textbook Question
When a thin glass tube is put into water, the water rises 1.4 cm. When the same tube is put into hexane, the hexane rises only 0.4 cm. Explain.
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Ch.11 - Liquids, Solids & Intermolecular Forces
Chapter 11, Problem 55
Why does spilling room-temperature water over your skin on a hot day cool you down while spilling room-temperature vegetable oil does not?
Verified step by step guidance1
Understand that the cooling effect of water is primarily due to the process of evaporation. When water evaporates, it absorbs heat from the surroundings (in this case, your skin) to change from a liquid to a gas, which cools the surface.
Recognize that water has a high heat of vaporization, meaning it requires a significant amount of energy to evaporate. This energy is taken from your skin, thus cooling it down.
Consider the properties of vegetable oil. Unlike water, vegetable oil has a much lower tendency to evaporate at room temperature because it has a higher boiling point and lower vapor pressure.
Since vegetable oil does not evaporate easily, it does not absorb heat from your skin in the same way water does. Therefore, it does not provide the same cooling effect.
Conclude that the key difference lies in the evaporation process: water evaporates readily at room temperature, absorbing heat and cooling the skin, while vegetable oil does not.
Related Practice
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.
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 is the heat of vaporization of water greater at room temperature than at its boiling point?
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.)