[SymeAaro (OP)]

Hello,
Just been thinking, and I was wondering about how a substance changes state. If heat is applied, the energy is used to break forces of attraction between the molecules, changing its state. I was thinking, however, could other types of energy be used to do this? Or just is it heat? Could, say, electrical or sound energy do the trick?
Thanks

[Kryptid]

Heat is just a form of molecular kinetic energy. Any form of energy you use to change a solid into a liquid ultimately does so because that energy is converted into molecular vibrations, rotations and other forms of movement (i.e. heat).

[chiralSPO]

Pressure is the other common variable for changing states. Most standard phase diagrams involve temperature and pressure as the phase-determining parameters (neither of which are energy, however thermal energy can be added to increase the temperature, and work can be done to increase the pressure, provided there is also a change in volume)

This will work for interconverting between solid (there can be multiple types of solid, depending on the substance), liquid, gas, and supercritical fluid.

More exotic phases can be achieved using other means. Ionized gases (plasmas) can be formed through heating alone, but it is often easier to use electric or magnetic fields (static or dynamic) to get enough energy into the matter. Spin states can be manipulated using magnetic fields (some matter can be magnetized in different ways, which counts as being in different states). Or electronic states can be changed using light or electric fields (this typically only produces very short-lived excited states that then relax back down, but constant illumination or in special cases where the excited state is long-lived can get around that. For instance MOSFET transistors are electronic insulators under standard conditions, but when an electric field is applied, they become conductive (note: the whole transistor is made of multiple components, but the semiconductor that is key to the operation of a transistor is a pure substance that undergoes a sort of "phase change" when an electric field is applied)

[evan_au]

Could other types of energy except heat change a state?

One example is where a partial phase change occurs due to changes in pressure, not strictly the pressure itself. Cornflour in water is a "shear-thickening liquid" - the action starts at 2 minutes.

Another case is superconductors, where an external  magnetic field can switch it from superconductor to normal conductor (or even insulator).

A case which was theorised (but later proven wrong) was in ice-skating; the theory said that solid ice becomes a thin film of liquid when the weight of the skater is focussed onto a small area by the thin blade of the skate. However, it is actually due to the outermost layer of molecules on the ice, which is in a semi-liquid state, rather than fully bound into an ice crystal.
https://en.wikipedia.org/wiki/Ice_skating#Physical_mechanics_of_skating

[wolfekeeper]

Thinking more broadly, when you electrolyse water you start with liquid and end up with gases.

[chiralSPO]

Thinking more broadly, when you electrolyse water you start with liquid and end up with gases.

This is an example of a chemical reaction. As I understand it, typically "changing state of matter" is meant to mean physical changes (where no covalent chemical bonds are formed or broken--solid, liquid, gaseous, and supercritical water are all unaltered H₂O molecules, just arranged and interacting in different ways).

This is a purely semantic classification (one could easily argue that chemical reactions are changes of state in which no remain unaltered, just arranged in different ways). The difference between a gas and a plasma could well be considered chemical as well... But it is a fairly useful distinction--I don't much care whether my water has a lot of ice in it or not, because it's all the same compound, but I would be quite distressed to learn that the 10L water jug in my office water cooler was filled with hydrogen and oxygen!

[PmbPhy]

This is a really cool thread with an awesome question!! I love it!

Just been thinking, and I was wondering about how a substance changes state.

All those responses and yet nobody has mentioned the most obvious and trivial example, i.e. energy from the sun in the form of radiation, i.e. light. When light hits snow it causes it to melt.

Perhaps I'm the one who thought of it because I live in New England and was hit be a snow storm recently and am now watching the snow melt by the Sun. There is no substitute for experience, right? Lol!!

Regarding changes of state by pressure. A simple example (which comes to mind since I'm in a region of the world which is in winter mode) is the fact that when a person is skating on ice the skate exerts a large pressure on the ice which melts it and that's what allows a person to skate. Cool, huh?

For details please see:http://mini.physics.sunysb.edu/~marivi/TEACHING-OLD/PHY313/doku.php?id=lectures:6

The author refers to it as "pressure melting". Nice name!

[deroan]

In processes not related to changes in the chemical composition of matter, the energy does not change and remains constant.