Question

How do I calculate vapor pressure of water?

Answer 1

You could use Antoine's equation to calculate the vapor pressure of water. Antoine's equation is a vapor pressure equation that describes the relationship between vapor pressure and temperature for pure components. So,

`log_10p = A - B/(C + T)`, where

`p` - the vapor pressure;
`T` - temperature;
`A`, `B`, `C` - constants specific to each substance.

You'd get `p = 10^(A-B/(C + T))`.

This equation is usually used with two sets of paramaters, a low-pressure paramater that describes the vapor pressure curve up to the normal boiling point, and a second paramater that covers the range from boiling point to critical point.

So, for water, the two sets of paramaters are

SET 1. `A` = 8.07131, `B` = 1730.63, `C` = 233.426 for temeperatures between `1` and `100^@C`;
SET 2. `A` = 8.14019, `B` = 1810.94, `C` = 244.485 for temperatures betwen `99` and `374^@C`.

Notice that you can use both sets of paramaters for temeperatures between `99` and `100^@C`.

Here's a diagram of what an Antoine curve would look like