Introduction to Entropy Check-In

Entropy increases from solid, liquid to gas. Why?

• Molecular disorder increases
• Molecular randomness decreases
• Molecules are more energetic
• Molecules are more reactive

Predict the entropy change, ΔS.

• ΔS = +
• ΔS = -
• ΔS = 0
• ΔS = no change

Predict the entropy change, ΔS.

• ΔS = +
• ΔS = -
• ΔS = 0
• ΔS = no change

Predict the entropy change, ΔS.

• ΔS = +
• ΔS = -
• ΔS = 0
• ΔS = little change

As NaCl dissolves according to the equation
NaCl(s) → Na+(aq) + Cl-(aq), the entropy of the system 

• Increases
• Decreases
• Remains the same

Which one of these would result in a decrease in entropy?

• A solid solute dissolves in water.
• A gas is released.
• A liquid freezes.
• A liquid boils.

Solid magnesium dissolves in an aqueous solution of hydrochloric acid, releasing hydrogen gas and heat from a solution of magnesium chloride. What is the sign on ΔS for this reaction?

• Negative because it is becoming more ordered.
• Negative because it is becoming more disordered.
• Positive because it is becoming more ordered.
• Positive because it is becoming more disordered.

Calculate the standard entropy change, ΔS°, for the reaction below.
2 H₂O (l) →2 H₂ (g) + O₂ (g)
H₂O (l): 69.91 J/(mol⋅K)
H₂ (g): 130.58 J/(mol⋅K)
O₂ (g): 205.0 J/(mol⋅K)

• 326 J/K
• -326 J/K
• 266 J/K
• -266 J/K

Calculate the standard entropy change, ΔS°, for the reaction below.
Al₂O₃ (s) + 3 H₂ (g) → 2 Al (s) + 3 H₂O (g)
Al₂O₃ (s): 51.0 J/(mol⋅K)
H₂ (g): 130.58 J/(mol⋅K)
Al (s): 28.32 J/(mol⋅K)
H₂O (g): 188.83 J/(mol⋅K)

• 35.6 J/K
• -35.6 J/K
• 180. J/K
• -180. J/K