In: Physics
An 8.5 g ice cube at −10°C is put into a Thermos flask containing 150 cm3 of water at 30°C. By how much has the entropy of the cube-water system changed when equilibrium is reached? The specific heat of ice is 2220 J/kg · K. (The latent heat of fusion for ice is 333 kJ/kg and the specific heat of water is 4187 J/kg · K.)
The change in entropy in this case is
ΔS1 = integral ( dQ /T)
=
m Cice ln (Tf / Ti)
=
(8.5 x 10-3) (2220) ln (273 / 263)
=
0.704 J/ K
Now the ice melts at 0oC , Then
ΔS2 = Q / T = mL
/T = 8.5 * 333 / 273 = 10.4 J /K
Now the water warms to lake temperature
ΔS3 = m Cw ln(Tf /
Ti)
=
(1000)(1.5*10-4 )(4187) ln (293 / 273)
=
44.4 J /K
Therefore total change in entropy
ΔS = 56.1 J /K