Question

water has an unusually high heat of vaporization (-40+kj/mol), allowing it to be used for evaporative cooling. what do you think would happen if a different compound was used for evaporative cooling - for example, methane (-8kj/mol)

Answer 1

If a different compound with a lower heat of vaporization than water, such as methane, were used for evaporative cooling, it would be less effective in absorbing heat and providing cooling since less energy is required for it to evaporate.

Step-by-step explanation:

Water's high heat of vaporization stands at 40.65 kJ/mol, which is essential for evaporative cooling. This high amount of energy is required to break the hydrogen bonds between water molecules, allowing liquid water to turn into water vapor. When water evaporates, especially at temperatures below its boiling point, it takes more energy, resulting in a cooling effect as this energy is taken from the surroundings.

Using a compound with a lower heat of vaporization, like methane at -8kJ/mol, would mean less energy is needed for the phase transition from liquid to gas. As a result, methane's cooling effect would be less significant compared to water because it would absorb less heat from its surroundings during evaporation.

Moreover, high humidity can inhibit the evaporation of water, leading to reduced cooling effect and potentially increased body temperatures in organisms that rely on perspiration for temperature regulation.

Answer 2

A lesser amount of heat will be drawn up from the mass to be cooled per unit mole of the new liquid vaporized, compared to the amount of heat that will be drawn by vaporizing a unit mole of water. For the case of methane, five mole of methane needs to be vaporized to get the same cooling effect of a mole of water.

Step-by-step explanation:

For a liquid like water to vaporize, it must draw a certain amount of energy from the surrounding in order for some of its molecules to gain enough energy to break out of the surface of the liquid as gas. If the heat of vaporization of water is about -40 kJ/mol, it means that for a mole of water to change from liquid to gas, it must draw up 40 kJ worth of heat from its surrounding. The effect is that the surrounding mass losses 40 kJ worth of heat, and cools down. If we should now use a new liquid, say methane with heat of vaporization of about -8kJ/mol, five moles of methane needs to be vaporized to get the same cooling effect of vaporizing a mole of water; since the heat that will be drawn by a mole of the methane is just bout 8 kJ.