Why is it incorrect to say that the boiling point of a substance is 100 C?

Question

Luna Chen · Accepted Answer

since you are ignorant of the substance's nature. A boiling point is intrinsic to what the substance even is. If it's table salt, then the boiling point is much higher than #100^@ "C"#. If it's ammonia, then the boiling point is negative!

Caleb Adams · Answer

Perhaps because you haven't specified a pressure?

We usually quote the #"normal boiling point"#; i.e. the temperature at which the vapour pressure of the solution reaches #1# #"atmosphere"#, and bubbles of vapour form directly in the liquid. This is the #"normal boiling point"# by definition. But we could perform a vacuum distillation, such that at LOWER temperatures than the #"normal boiling point"#, the vapour pressure of the liquid is such that it is equal to the ambient pressure, and it distills over. I grant that the pressure here is likely one atmosphere (and that the substance is water), BUT we don't KNOW this for #"shure"#. Are you happy with this. I would certainly try to take this definition of #"boiling point"# on board, especially if you are an undergrad.

Olivia Anton · Answer

It changes with change in pressure.

Kai Bowman · Answer

undefined It is incorrect to say that the boiling point of a substance is 100°C because the boiling point varies depending on the atmospheric pressure. The boiling point of water at standard atmospheric pressure (1 atmosphere) is indeed 100°C, but this value changes with altitude and pressure. For example, at higher altitudes where atmospheric pressure is lower, the boiling point of water is lower than 100°C, and conversely, at higher pressures, the boiling point is higher than 100°C. Therefore, stating that the boiling point of a substance is always 100°C is inaccurate because it does not account for variations in pressure.