-1
$\begingroup$

For each of the following pairs, choose the member with the lower boiling point. Explain your reason in each case.

HI(g) or HCl(g)

If they were both aqueous solutions, I would know that HCl has a lower boiling point. But the question specifically mentions gas. I believe that gas can't have a boiling point.

Can anyone help me with this?

$\endgroup$
  • 7
    $\begingroup$ When you make it cold enough, a gas will become liquid; that is also the boiling point. $\endgroup$ – Martin - マーチン Nov 8 at 15:05
  • 1
    $\begingroup$ Every gas has the boling point. Substances considered as a (permanent) gas have their boiling point below the room temperature. The lowest boiling poist has helium-4, near 4.2 K. $\endgroup$ – Poutnik Nov 8 at 16:58
0
$\begingroup$

I believe that gas can't have a boiling point.

The boiling point of a substance refers to the phase transition between pure liquid and pure gas. It depends on the pressure of the system, and the normal boiling point is taken at standard pressure, 101.3kPa (1 atm).

All pure substances that occur in a liquid and a gas state have boiling points. Some substances skip the liquid state and go directly from solid to gas (e.g. carbon dioxide at standard pressure). Some substances decompose before they boil when you heat up the liquid.

So the substance has the boiling point, not the gas. You could argue whether a pure liquid has a boiling point (you can't measure the boiling point without having gas present as well).

If they were both aqueous solutions, I would know that HCl has a lower boiling point.

Solutions (homogeneous mixtures) are more complicated than pure substances when it comes to boiling. Usually, the composition changes because one substance transitions preferentially into the gas phase. For example, if you boil maple sap (an aqueous solution of sugars and other solutes), the temperature at which the solution boils will increase during the process as the concentration of sugar increases. In this case, there is no fixed boiling point because it depends on composition.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.