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Physics, Astronomy & Cosmology / shape change with no energy transfer?
« on: 11/05/2022 23:02:58 »
As an aside from the discussion on energy transfer between ice and water, consider a cube of ice immersed in water, all at 0 deg C.
All the molecules are jiggling about at random. Those at the edges and corners of the cube have the fewest bonds to other members of the cube so are most likely to acquire sufficient kinetic energy to leave the solid and enter the liquid.
It takes 334 joule/gram (latent heat of fusion) x 3 x 10-23 gram (mass of a water molecule) to release one molecule from ice. So by leaving, our exceptionally energetic molecule reduces the temperature (the average kinetic energy of all the remaining molecules) of the ice by a tiny amount.
So a water molecule could now attach itself to the ice to restore thermal equilibrium. But the most probable place for the impact to occur is on a flat surface, not an edge.
Thus if we maintain absolute equality of temperature between the ice and the water, the cube will gradually turn into a sphere!
All the molecules are jiggling about at random. Those at the edges and corners of the cube have the fewest bonds to other members of the cube so are most likely to acquire sufficient kinetic energy to leave the solid and enter the liquid.
It takes 334 joule/gram (latent heat of fusion) x 3 x 10-23 gram (mass of a water molecule) to release one molecule from ice. So by leaving, our exceptionally energetic molecule reduces the temperature (the average kinetic energy of all the remaining molecules) of the ice by a tiny amount.
So a water molecule could now attach itself to the ice to restore thermal equilibrium. But the most probable place for the impact to occur is on a flat surface, not an edge.
Thus if we maintain absolute equality of temperature between the ice and the water, the cube will gradually turn into a sphere!