Dry ice, sometimes referred to as "cardice" or as "card ice" (chiefly British English), is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue (other than incidental frost from moisture in the atmosphere). Dry ice sublimates at
°C (
°F) at Earth atmospheric pressures. Which of the following statements is correct about the sublimation of dry ice? (
,
and
mean the change in enthalpy, entropy and Gibbs free energy, respectively.)
a) and , and for all temperatures.
b) and , and for all temperatures.
c) and , and for all temperatures.
d) and , and for high temperatures.
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Since it is a cooling agent, It is absorbing heat to convert into its gaseous form. Hence Δ H > 0
Also, since it is converting from Solid to Gas, the Entropy Increases. Hence Δ S > 0
Now,
Δ G = Δ H − T Δ S
To ensure Δ G < 0 , the term T Δ S must dominate over the Δ H term (since both Δ H and Δ S are positive)
And for that to happen, it is favorable to have the temperature as highly positive as possible..
Hence, the answer is ( D )