Question

What would occur if water were heated on the moon?

`"A. the water would rapidly vaporize;"`
`"B. boiling point of water WOULD decrease relative to that at 1 atm;"`
`"C. boiling point of water WOULD increase relative to that at 1 atm;"`
`"D. no conclusions may be drawn."`

Answer 1

`A.` ##The water sample will boil with alacrity.

Explanation:

The boiling point of any liquid is the temperature at which the vapour pressure of the liquid is equal to the ambient pressure, and bubbles of vapour form directly in the liquid. Normally, we speak of the normal boiling point, where the ambient pressure is `1*atm`.

In a hard vacuum, however, such as would occur on the moon, the boiling point of a liquid would be much less than the normal boiling point, in that the temperature does not have to be raised so much so that the vapour pressure is equal to (or exceeds that of) the external pressure. I suspect that if you opened a bottle of water on the moon, it would be like the scenario when you open a can of soft drink that you have shook up, i.e. a fountain.

Answer 2

`A.` ##The water sample will boil with alacrity.

Explanation:

The boiling point of any liquid is the temperature at which the vapour pressure of the liquid is equal to the ambient pressure, and bubbles of vapour form directly in the liquid. Normally, we speak of the normal boiling point, where the ambient pressure is `1*atm`.

In a hard vacuum, however, such as would occur on the moon, the boiling point of a liquid would be much less than the normal boiling point, in that the temperature does not have to be raised so much so that the vapour pressure is equal to (or exceeds that of) the external pressure. I suspect that if you opened a bottle of water on the moon, it would be like the scenario when you open a can of soft drink that you have shook up, i.e. a fountain.