Question

Some ice at -5 degrees Celsius is used to cool a cup of water? What happens to the entropy of the ice, water and (water + ice)? Please explain for each ice, water and water+ice.

a. increase

b. decrease

c. remain the same

d. none of the above

Answer 1

Ice: The Entropy increases. Since the thermal energy increases the bonds between the molecules become week and thus start melting. The thermal vibrations results to the increase in the entropy.

ΔS = ΔQ/T , where S : Entropy, Q: Heat energy, T: Temperature.

Since ice is gaining energy, ΔQ is positive. So ΔS is positive which means that the final entropy is larger than the initial entropy, which means that the entropy increases.

Water: Entropy decreases. Since the thermal energy decreases the bonds between the molecules become stronger and thus start freezing. The decrease in thermal vibrations results to the decrease in the entropy.

(water + ice) : The water and ice system come to the equilibrium state at which the net heat transfer is zero which means ΔQ comes to zero, which results in the entropy to be constant and remains the same.