Internal energy!

[chocofingers]

Could anybody tell whether the internal energy in the below mentioned processes is increasing , decreasing or remains the same!
And please provide explanation as well!

a) water freezing at constant temperature
b) stone falling under gravity in a vacuum
c) water evaporating at constant temperature
d) stretching a wire at constant temperature

What I believe is that it would increase in processes c & d. ???

[yinx]

i might be wrong, but internal energy is dependent on temperature change. If temperature is constant, there should not be any change in internal energy. no?

[chocofingers]

yeah I too thought the same... but during melting internal energy increases ... why?? although the temperature is constant ///

[Drakkith]

yeah I too thought the same... but during melting internal energy increases ... why?? although the temperature is constant ///

To change the phase from solid to liquid, it takes an input of energy. This energy only causes the materiel to melt, not to increase in temperature. Once the materiel has liquified, any further energy will cause the temperature to rise again. Same thing happens when it transitions to a gas from a liquid.

[chocofingers]

To change the phase from solid to liquid, it takes an input of energy. This energy only causes the materiel to melt, not to increase in temperature. Once the materiel has liquified, any further energy will cause the temperature to rise again. Same thing happens when it transitions to a gas from a liquid.

So it means that during melting,boiling or any such process, internal energy remains constant ???

[yinx]

I think what drakkith is saying is, internal energy does increase in melting process as there is an input of heat energy to the substance, however temperature remains constant while melting.

[chocofingers]

okey thanyou, yinx & drakkith... I got it :)

[dorebase2006]

This may help: http://www.physicsforums.com/showpost.php?p=2302925&postcount=3

[chocofingers]

thnxz dorebase...