Practice: Entropy and Free Energy

Entropy is a measure of

• acidity of a sample

• disorder of a system

• concentration of a solution

• chemical activity of an element

Which 1 mole sample has the least entropy?

• Br₂(s) at 266K

• Br₂(l) at 266K

• Br₂(l) at 332K

• Br₂(g) at 332K

Which of these changes produces the greatest increase in entropy?

• CaCO₃(s) → CaO(s) + CO₂(g)

• 2Mg(s) + O₂(g) → 2MgO(s)

• H₂O(g) → H₂O(l)

• CO₂(g) → CO₂(s)

As H₂O(l) is added to KNO₃(s) to form KNO₃(aq), the entropy of the system

• increases

• decreases

• remains the same

Which sample has the greatest entropy?

• NH₃ (g)

• NH₃ (l)

• NH₃ (s)

• NH₃ (aq)

A reaction must be thermodynamically favorable if it is

• endothermic and an increase in entropy

• endothermic and an decrease in entropy

• exothermic and an decrease in entropy

• exothermic and an increase in entropy

Which one of the following processes produces a decrease in the entropy of the system?

• Dissolution of solid KCl in water

• Mixing of two gases into one container

• Freezing water to form ice

• Melting ice to form water

For the reaction C₂H₆ (g) → C₂H₄ (g) + H₂ (g),

ΔH^ο is +137 kJ/mol and ΔS^οis +120 J/K⋅mol. This reaction is

• thermodynamically unfavorable at all temperatures

• thermodynamically favorable only at low temperature

• thermodynamically favorable only at high temperature

• thermodynamically favorable at all temperatures

A reaction that is not spontaneous at high temperaturse can be thermodynamically favorable at low temperatures if ΔH is __________ and ΔS is __________.

• +, +

• -, -

• +, -

• -, +

Which combination of ΔH and ΔS NEVER has a spontaneous reaction?

• +ΔH and +ΔS

• +ΔH and -ΔS

• -ΔH and -ΔS

• -ΔH and +ΔS