Write down an equation that shows by how much the molar free energy of solid Cu is increased when it is present as a small sphere of radius r in liquid Cu. By how much must liquid Cu be cooled below Tm before a solid particle of Cu can grow if the particle diameter is (i) 2 um, (ii) 2 nm? (Cu: Tm is 1085 C, atomic weight is 63.5, density is 8900 kg m-3, solid/liquid interfacial energy Y = 0.144 J m-2, latent heat of melting L = 13300 J mol-1)