What is distiction between melting and sublimation?

Question

If you think that you know the difference, try this:

is phase transition between solid helium and
its other non-crystalline phase at 8 Kelvin
melting or sublimation?

Phase diagram can be seen at

http://www.britannica.com/eb/art-17954

Answer 1

Melting is when a solid becomes a liquid. Sublimation is when a solid becomes a gas without first becoming a liquid.

Since helium's melting point is less than 1K, by simple process of elimination I would say your answer there is sublimation.

Answer 2

Melting is the transition from solid to liquid.
Sublimation is the transition from solid to gas without passing through a liquid state. Dry ice at room temperature is the best known example.

I don't have a phase diagram of helium, but it forms a solid only at high pressure (2.5 MPa), at .95K, and boils at 4.22K, so it's unlikely to be anything other than gas at 8K.

Answer 3

Melt=change from solid to liquid. Ex ice to water.
Sublime=change from solid to vapor. Ex dry ice to CO2 gas.

not knowing the critical temperature of He, I can't answer the 2nd question. If you are above Tc, It probably has a different name.

Answer 4

MELTING AND SUBLIMATION ARE BOTH ACTIVITIES THST TAKE PLACE DUE TO CHANGE IN TEMPERATURE MELTIN IS A PROCESS WHERE A SOLID CONVERTS INTO LIQUID ON HEATING WHEREAS SUBLIMATION IS A PROCESS WHERE A SOLID DIRECTLY CONVERTS INTO GAS WITHOUT GETTING CONVERTED INTO LIQUID.