Question

Classify the phase changes by the signs of the system's AH and AS.

a. AH = +and 4S = +
b. AH =+and 4S =
c. AH = -and 4S = +
d. AH = -and 4S =

Answer Bank
a. liquid to solid
b. gas to liquid
c. solid to liquid
d. gas to solid
e. solid to gas
f. liquid to gas

Answer 1

The signs of AH and AS can be used to classify phase changes.

Step-by-step explanation:

The signs of the system's AH and AS can be used to classify phase changes. Here are the classifications for each sign combination:

1. AH = + and AS = +: The phase change is from solid to liquid. Example: Ice melting into water.
2. AH = + and AS = 0: The phase change is from gas to liquid. Example: Water vapor condenses into liquid water.
3. AH = - and AS = +: The phase change is from solid to gas. Example: Dry ice sublimates into carbon dioxide gas.
4. AH = - and AS = 0: There is no specific phase change associated with this sign combination.

Answer 2

Phase changes are classified according to the signs of ΔH and ΔS. Positive ΔH and ΔS indicate a liquid to gas transition, positive ΔH and negative ΔS signify a liquid to solid transition, negative ΔH and positive ΔS correspond to solid to liquid, and negative for both represents gas to liquid.

Step-by-step explanation:

To classify the phase changes by the signs of the system's ΔH and ΔS, we consider the energy (enthalpy, ΔH) and entropy (ΔS) associated with each phase change. A positive ΔH indicates an endothermic process where heat is absorbed, and a positive ΔS indicates an increase in disorder or entropy.

• a. ΔH = + and ΔS = +: This suggests a transition to a more disordered and higher energy state, such as liquid to gas (e).
• b. ΔH = + and ΔS = -: Heat is absorbed, but the disorder decreases, typically in a liquid to solid transition (a).
• c. ΔH = - and ΔS = +: Energy is released in this exothermic process, and disorder increases, like solid to liquid melting (c).
• d. ΔH = - and ΔS = -: Energy is released and disorder decreases, indicating a gas to liquid condensation (b).

To directly answer the question:

1. ΔH = + and ΔS = + corresponds to liquid to gas (f).
2. ΔH = + and ΔS = - corresponds to liquid to solid (a).
3. ΔH = - and ΔS = + corresponds to solid to liquid (c).
4. ΔH = - and ΔS = - corresponds to gas to liquid (b).