- #1
Pranav Jha
- 141
- 1
If we melt ice at 0'C to water at 0C, what is the change in the internal energy of the ice-water system?
As per the first law of thermodynamics, ΔU = ΔQ +ΔW
where they are increase in internal energy, heat flow to the system and work done on the system respectively.
If we melt ice at 0C, we have to supply heat to the system, so Q is positive
My initial thought on change in internal energy would have been that, as we melt a solid to liquid, there is increase in intermolecular distance resulting in increase in potential energy of the system BUT ice is less dense than water. So,the intermolecular spacing actually decreases when ice melts to water resulting in decrease in potential energy.
As U= K.E. + P.E.
and as K.E. is constant due to the constant temperature, U has to decrease due to decrease in potential energy
Further, the ice contracts on melting (due to the greater density of water), so the atmosphere actually does work on ice when it melts to a smaller volume of water. So, work done on the system is positive.
Therefore, we have a decrease in potential energy, increase in heat energy and increase in work done on the system.
So, what is the net effect on the internal energy of the system?
I believe my reasoning on work done and decrease in potential energy could be flawed as well. So, please help me out with this thought process.
As per the first law of thermodynamics, ΔU = ΔQ +ΔW
where they are increase in internal energy, heat flow to the system and work done on the system respectively.
If we melt ice at 0C, we have to supply heat to the system, so Q is positive
My initial thought on change in internal energy would have been that, as we melt a solid to liquid, there is increase in intermolecular distance resulting in increase in potential energy of the system BUT ice is less dense than water. So,the intermolecular spacing actually decreases when ice melts to water resulting in decrease in potential energy.
As U= K.E. + P.E.
and as K.E. is constant due to the constant temperature, U has to decrease due to decrease in potential energy
Further, the ice contracts on melting (due to the greater density of water), so the atmosphere actually does work on ice when it melts to a smaller volume of water. So, work done on the system is positive.
Therefore, we have a decrease in potential energy, increase in heat energy and increase in work done on the system.
So, what is the net effect on the internal energy of the system?
I believe my reasoning on work done and decrease in potential energy could be flawed as well. So, please help me out with this thought process.