19. Chemical Thermodynamics

An ideal gas is allowed to expand at constant temperature. What are the signs of ∆H, ∆S & ∆G.

Consider the freezing of liquid water at 30^°C. For this process what are the signs for ∆H, ∆S, and ∆G?

Predict the sign of ∆S in the system for each of the following processes:

a) Ag⁺ (aq) + Br ^- (aq) → AgBr (s)

b) CI₂ (g) → 2 CI ^- (g)

c) CaCO₃ (s) → CaO (s) + CO₂ (g)

d) Pb (s) at 50^°C → Pb (s) at 70^°C

For each of the following reactions state the signs of ∆H (enthalpy) and ∆S (entropy):

a) Fusion of ice.

b) Sublimation of CO₂

c) Vaporization of aqueous water.

d) Deposition of chlorine gas.

e) Condensation of water vapor. 

Diethyl ether (C₄H₁₀O₂, MW = 90.1 g/mol) has a boiling point of 35.6^oC and heat of vaporization of 26.7 kJ/mol. What is the change in entropy (in kJ/K) when 3.2 g of diethyl ether at 35.6^oC vaporizes at its boiling point?

2 NH₃ (g) + 2 O₂ (g) → NH₄NO₃ (s) + H₂O (l)

2 NO (g) + O₂ (g) → 2 NO₂ (g)

Which reaction is most likely to have a positive ∆S of reaction?

a) SiO₂ (s)  +  3 C (s)  →  SiC (s)  +  2 CO (g)

b) 6 CO₂ (g)  +  6 H₂O (g)  → C₆H₁₂O₆ (s)  +  6 O₂ (g)

c) CO (g)  +  Cl₂ (g)  → COCl₂ (g)

d) 3 NO₂ (g)  +  H₂O (l)  → 2 HNO₃ (l)  +  NO (g)

Identify sign of entropy changes for the following processes.

1) freezing water to form ice

2) ideal gas allowed to expand in a closed container at constant T

3) mixing of two gases into one container

4) NH₂ (g) (1atm) → NH₂ (g) (3 atm)

5) gas mixture transferred from larger to smaller container

Select correct statement(s) below:

a) gaseous CO₂ has higher entropy in 2 L container compared to in 5 L container

b) N₂O (g) contains higher standard molar entropy then HI (g)

c) NaHCO₃ (aq) + HC₂H₃O₂ (aq) → NaC₂H₃O₂ (aq) + H₂O (l) + CO₂ (g) has a negative ∆S

d) evaporation of water at 100 °C involves greater ∆S than evaporation at 112 °C

Entropy is the measure of ________ in a system.

What will the sign on ∆S be for the following reaction and why? 2 Mg(s) + O₂(g) → 2 MgO(s)

Classify the phase changes by the signs of the system's ΔH° and ΔS°.

Which of the following has the largest standard molar entropy, S° (298.15 K)?

Consider the following standard entropies at 298 K: Br2(𝑙) 152.3 J/mol-K, Br2(𝑔) 245.3 J/mol-K, I2(𝑆) 116.7 J/mol-K, I2(𝑔) 260.6 J/mol-K. Which of the following statements about these entropies is or are true?

a. The standard entropy of I2(𝑔) is greater than that of I2(𝑆) because gases have more degrees of freedom than do solids.

b. The standard entropy of I2(𝑔) is greater than that of Br2(𝑔) because 𝐼2 has a higher molar mass than does Br2.

c. The standard entropy of Br2(𝑙) is greater than that of I2(𝑆) because Br is more electronegative than I.