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