Open Question
What is ΔS° for the reaction between nitrogen gas and fluorine gas to form nitrogen trifluoride gas, and how can the sign of ΔS° be rationalized?
19. Chemical Thermodynamics
Entropy
Multiple Choice
For each of the following reactions state the signs of ∆H (enthalpy) and ∆S (entropy):
a) Fusion of ice.
b) Sublimation of CO2
c) Vaporization of aqueous water.
d) Deposition of chlorine gas.
e) Condensation of water vapor.
A
a) — b) — c) + d) — e) +
B
a) — b) — c) — d) — e) —
C
a) + b) + c) + d) — e) —
D
a) — b) — c) — d) + e) +
Verified step by step guidance1
Identify the type of process for each reaction: a) Fusion of ice is melting, b) Sublimation of CO2 is a solid turning into gas, c) Vaporization of aqueous water is liquid turning into gas, d) Deposition of chlorine gas is gas turning into solid, e) Condensation of water vapor is gas turning into liquid.
Understand the concept of enthalpy (∆H): For endothermic processes (absorbing heat), ∆H is positive. For exothermic processes (releasing heat), ∆H is negative.
Understand the concept of entropy (∆S): Entropy increases (positive ∆S) when disorder increases, such as when a substance changes from solid to liquid or liquid to gas. Entropy decreases (negative ∆S) when disorder decreases, such as when a substance changes from gas to liquid or liquid to solid.
Apply these concepts to each reaction: a) Fusion of ice involves solid to liquid, so ∆H is positive and ∆S is positive. b) Sublimation of CO2 involves solid to gas, so ∆H is positive and ∆S is positive. c) Vaporization of aqueous water involves liquid to gas, so ∆H is positive and ∆S is positive.
Continue applying these concepts: d) Deposition of chlorine gas involves gas to solid, so ∆H is negative and ∆S is negative. e) Condensation of water vapor involves gas to liquid, so ∆H is negative and ∆S is negative.
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