Answer 2:
All elements can exist in 3 states--if you can adjust the temperature and pressure they experience at will.
Let's unpack that starting with an element which is abundant and with which we are somewhat familiar: nitrogen.
Earth's atmosphere is made up of 78% gaseous nitrogen, N2, so we know that the gaseous form of nitrogen is stable at room temperature (20 C for argument's sake) and atmospheric pressure (0.1 MPa = 0.1 x 106 Pa, where Pascals are a unit of pressure). Liquid nitrogen is used as an industrial coolant (think early COVID-19 vaccines) because--drum roll--it is stable at low temperatures at atmospheric pressure (-196 C to be exact, and still 0.1 MPa). Nitrogen freezes solid at -210 C under atmospheric pressure. So if you could cool the nitrogen in the air down from 20 C, it would take a while but you'd reach the liquid's temperature at -196 C, and the solidus temperature at -210 C. But what if you could also change the pressure?
Hypothesize with me: At a constant temperature of -190 C (where gaseous nitrogen is stable at atmospheric pressure) would increasing the pressure change which state is stable? Hint: liquid nitrogen is more dense than gaseous nitrogen.
Did you say yes? If so, you're right! Increasing the pressure at this temperature tends to stabilize the liquid state of nitrogen. Now, if the density of liquid nitrogen is very similar to the density of solid nitrogen, what effect would increasing the pressure on liquid nitrogen at -200 C have? Did you say none? It's none! Increasing the pressure will not cause liquid nitrogen to solidify because of the negligible density difference between the solid and the liquid at -200 C.
We can conduct similar analyses for other elements, but it is important to note the following: just as equilibrium state (solid, liquid, gas) is a function of temperature and pressure, density is a function of temperature and pressure as well! Click Here to return to the search form.
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