# Does the rate of which something melts/vaporizes increases with heat?

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## Main Question or Discussion Point

Something I've been thinking about recently is like how much heat would it take to evaporate an entire lake in less than a second. Or something like Tungsten Steel. The main question is does an increase in heat increase the rate of its change in structure?

Sorry for the boring question.

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berkeman
Mentor
Welcome to the PF.
Something I've been thinking about recently is like how much heat would it take to evaporate an entire lake in less than a second.
That would take the heat of a large explosion, which would have kinetic dispersive effects at the same time.
Or something like Tungsten Steel.
The rate of melting of steel would indeed depend on the input of energy per unit time (power). The energy input for phase change (solid to liquid melting) is part of the study of thermodynamics. Wikipedia is a good source for the basic information on melting and phase changes and thermodynamics.
does an increase in heat increase the rate of its change in structure?
Yes, see above.

Lnewqban and sophiecentaur
That would take the heat of a large explosion, which would have kinetic dispersive effects at the same time.
Kinetic Dispersive effects? Do you mind elaborating on this?

berkeman
Mentor
Kinetic Dispersive effects? Do you mind elaborating on this?
Well, I think the only real-world scenario to evaporate a lake in a second or few is from a meteor impact or thermonuclear explosion, no? And although "heat" is part of that evaporation overall, the water would be ejected from the lake also by the shock waves before the heat vaporised it, I think. Boom!

https://c8.alamy.com/comp/DDG606/op...ter-baker-atomic-nuclear-explosion-DDG606.jpg

jrmichler
jrmichler
Mentor
Kinetic Dispersive effects? Do you mind elaborating on this?
If you could magically and instantaneously heat a lake to boiling, the steam would initially occupy the same space as the water. The steam would be under extremely high pressure, so it would expand rapidly. BOOM!

And @berkeman covered heating a lake without magic.

A good exercise is to calculate the total heat to evaporate the water from a small lake, then convert to an atomic bomb size in kilotons or megatons. Or size and velocity of a meteor.

...The main question is does an increase in heat increase the rate of its change in structure?

Sorry for the boring question.
Welcome!
Rather than boring, yours is a good question.
It seems that you are referring to a huge rate of transfer of thermal energy from one body to another.

https://en.m.wikipedia.org/wiki/Heat

sophiecentaur
Gold Member
The main question is does an increase in heat increase the rate of its change in structure?
We could interpret this question in mundane Engineering terms. The ratio of boiling of a kettle will depend on the Power rating of the element (of course?). Introducing extreme situations can change things but that basic idea must still apply.
If you could magically and instantaneously heat a lake to boiling, the steam would initially occupy the same space as the water.
And I think it would have to be 'magic'. I'm not sure if the state diagram of water would actually contain a T/P combination that sustained liquid and gas phases. In any case, the energy density would probably involve ionisation / separation so could you actually call the stuff liquid or gas? More like a plasma.

Any thermal transfer process depends on more than just the 'available power'. Clothes dry a lot quicker when they are moved around in a tumble dryer than if you just put them in front of a heater. It's a function of surface area (and convection / radiation in different cases) . The delay in thermal transfer in a nuclear explosion goes towards the mushroom image. Without convection (in space) the progress of any explosion is very different (even a candle won't burn easily in the ISS).

Lnewqban
Nugatory
Mentor
The main question is does an increase in heat increase the rate of its change in structure?....Sorry for the boring question.
No question that leads to a discussion of "kinetic dispersive effects" - with a picture! - is boring
And the energy calculation that @jrmichler suggests in #5 is a lot of fun.....

It takes a fixed amount of energy to change a given quantity of a given substance at a given temperature into liquid or gas, so the rate of change is going to depend on how quickly that amount of energy can be transferred.

Heat energy flows from high temperature to low temperatures, and the greater the temperature difference the faster the transfer, so all else being the same if you want to melt or vaporize something in a hurry you'll use high heat. That's why when I need to melt some ice in a hurry I put it in a pan over the stove (absorb heat from a 1000+ degree flame) instead of leaving it on the table (absorb heat from 20 degree air); the total amount of heat required is the same but it takes a lot longer to move it one way than the other.

Something I've been thinking about recently is like how much heat would it take to evaporate an entire lake in less than a second. Or something like Tungsten Steel. The main question is does an increase in heat increase the rate of its change in structure?

Sorry for the boring question.
Not boring, but not particularly clear what you're asking, either. Anybody who has a stovetop with Low and High settings could answer whether turning the heat up means the water boils faster or not.

The bit about a lake and tungsten-steel, that has more to do with delivery method than heat. Drop a big enough atomic bomb into a small enough lake and you'll definitely vaporize pretty much the whole thing within seconds... mostly through kinetic heat : all those molecules getting suddenly accelerated *much* faster than they're comfortable with.