Question

How would the boiling point of a liquid be affected if it is measured in a submarine 12,125 meters beneath the sea? What if it were measured on top of Mt. Rainer (4,392 meters high)?

Answer 1

The boiling point of a liquid is defined as the temperature at which the vapour pressure of the liquid equals the atmospheric pressure; i.e., the pressure around it. As the boiling point is the temperature at which the vapour pressure equals the atmospheric pressure, it varies with the altitude from the sea level (as the pressure varies). The normal boiling point of a liquid is measured at sea level, 1 atm pressure. At higher altitudes, such as on top of Mt. Rainer in this case, the atmospheric pressure is considerably lower as compared to that at the sea level, the liquid would have a lower boiling point when compared to that measured under normal altitudes closer to the sea level. Similarly, below the sea level, as in a submarine 12,125 meters beneath, the surrounding pressure and the thus the boiling point would be higher than that at the sea level.

One can use the following equation to calculate boiling points at varying altitudes:

T= T₀- (0.00184 h) where h is the altitude from sea level in feet, T is the new and T₀ is the normal boiling points.

Here, on top of Mount Rainer(4392 metres or 14409.45 feet above), the boiling point of the liquid is given by:

T = T₀ - (0.00184 * 14409.45) = T₀-26.5; i.e., the liquid would boil at a temperature 26.5 °C lower than normal.

Similarly in the submarine (since below sea level, altitude is taken as negative, -12125 metres or -39780 feet)

, T= T₀- (0.00184* -39780)= T₀+ 73.20; i.e., the liquid would boil at a temperature 73.2 °C higher than normal.