Entropy and Gibbs Free Energy

An example of a process in which entropy decreases, yet is still thermodynamically favorable, is:

• Melting an ice cube at 25°C.

• Salt dissolving in a beaker of water at room temperature.

• Freezing an ice cube at -10°C.

• Heating a gas inside of a balloon.

Which process below is thermodynamically favorable?

• Aqueous Na+ and Cl- ions forming a solid in solution.

• A sample of radioactive carbon decaying over time.

• A ball rolling up a hill.

• An ice cube melting at -5°C.

Which statement below is true?

• A molecule of CH₄ has more entropy than a molecule of C₄H₁₀ at 25°C.

• A sample of NH₃(l) has more entropy than NH₃(g).

• A crystal of Mg at 0 K has more entropy than a crystal of Mg at 200 K.

• A sample of CO₂(g) has more entropy than CO₂(s).

Na₂SO₄(s) → 2 Na⁺(aq) + SO₄^-2(aq)

The change in entropy (ΔS) for this process is:

• Greater than 0.

• Less than 0.

• Equal to 0.

2 H₂(g) + O₂(g) → 2 H₂O(g)

The change in entropy (ΔS) for this process is:

• Greater than 0.

• Less than 0.

• Equal to 0.

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NGSS.HS-PS3-4

For which of these processes is the value of ΔS expected to be negative?

I. NaCl(s) is dissolved in water.

II. Steam condenses to liquid water.

III. MgCO₃(s) is decomposed into MgO(s) and CO₂(g).

• I only

• I and III

• II only

• II and III

What are the signs of the enthalpy change and entropy change, respectively, for the melting of ice?

H₂O(s) → H₂O(l)

• + , +

• - , -

• - , +

• + , -

Which of the following substances is expected to have the greatest entropy?

• H₂O(l)

• H₂O(g)

• H₂O₂(l)

• H₂O₂(g)

Which process is exothermic and occurs with a decrease in entropy?

• H₂O(l) → H₂O(s)

• H₂O(s) → H₂O(l)

• 2 H₂O(l) → 2 H₂(g) + O₂(g)

• H₂O(l) → H₂O(g)

Which of the following is true when CO₂(g) undergoes deposition to turn into CO₂(s) at -100°C and 1 atm?

• ∆H > 0, ∆S > 0

• ∆H < 0, ∆S < 0

• ∆H > 0, ∆S < 0

• ∆H < 0, ∆S > 0