AP Thermo 2 Review

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

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

Spontaneity is determined by....

• enthalpy only
• entropy only
• enthalpy and entropy
• enthalpy, entropy, and temperature

In a spontaneous process, ΔG°....

• always decreases
• always increases
• equals zero
• doesn't change

When a liquid boils what are the signs for Δ H  and  Δ S  ? (Think about H₂O as an example!)

• Δ H  =  +   Δ S  =  +
• Δ H  =  -   Δ S  =  -
• Δ H  =  +   Δ S  =  -
• Δ H  =  -   Δ S  =  +

Tags

NGSS.HS-PS1-4

     Predict the signs of  Δ H ,  Δ S and Δ G for the reaction:
  H₂ (g) → 2 H(g) 

• Δ H= -  ,  Δ S = +  and Δ G = - (all temps) 
• Δ H= +  ,  Δ S = +  and Δ G = -  (At all temps) 
• Δ H= +  ,  Δ S = +  and Δ G = -  (At low temps) 
• Δ H= +  ,  Δ S = +  and Δ G = -  (At high temps) 

Tags

NGSS.HS-PS1-4

The formation ½ A₂ + 2 B₂ + C → CAB₄ has an enthalpy (ΔH) of -104 kJ and a change in entropy (ΔS) of -60.8 J/K at 30 °C. What is the free energy and spontaneity of the reaction? (LOOK AT UNITS!!!)

• -85.6 kJ, spontaneous
• -18.3 kJ, not spontaneous
• +18.3 kJ, spontaneous 
• +85.6 kJ, not spontaneous