substances change phase when?

Question

Just need a little science help :>)

Answer 1

I assume you mean state of matter, as in solid liquid gas.
when the pressure and temperature on a substance is at the right level for solid, it is solid, right for liquid it's liquid, for gas it's gas it's different for every substance

for water, at 1atm pressure and 0 degrees C it changes from solid to liquid(ice melts) and back(water freezes)
at 1 atm 100 degrees C it changes from liquid to gas(boils) and back(water condenses)

even rocks go through this, just look at a volcano, not sure of the temps in there, but it's the same thing as ice melting, solid is changing to liquid, due to the right temp at the earths pressure.

besides heating it, you can boil water by lowering the pressure. you can get water to boil at 20 degrees C by lowering the pressure in a vacuum chamber...

so two ways to change state of matter, increase energy(heat it)
or let it expand(lower the pressure)

Answer 2

Substances change phases when they also change temperature. They go from solid to liquid and gas, when the temperature raises, and from gas to liquid and to solid when the temperature goes down.

Answer 3

The temperature changes.

the substance will change to a gas when it reaches boiling point, to a liquid above melting point, and to a solid at freezing point.