Carbon dioxide gas at (-78 ,^ C ) and 1 atm is allowed to deposit
CHEMISTRY · Single correct · A Level · Chemistry · Thermodynamics · Thermodynamics
Problem
Carbon dioxide gas at −78∘C and 1 atm is allowed to deposit, forming dry ice at the same temperature and pressure. Which of the following best explains the sign of the entropy change, ΔS, for the CO2 in this process?
(a) ΔS is zero because the temperature does not change, so the average kinetic energy—and thus entropy—remains the same.
(b) ΔS is negative because particles lose freedom of motion when a gas becomes a solid, decreasing matter dispersal.
(c) ΔS is positive because the heat released during deposition increases the dispersal of energy in the system.
(d) ΔS is positive because the solid occupies less volume, allowing more possible arrangements of particles per unit volume.