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

Without doing any calculations, determine the sign of ΔSsys for each chemical reaction. a. 2 KClO3(s) ¡ 2 KCl(s) + 3 O2( g)

Without doing any calculations, determine the signs of ΔSsys and ΔS surr for each chemical reaction. In addition, predict under what temperatures (all temperatures, low temperatures, or high temperatures), if any, the reaction is spontaneous. a. C3H8( g) + 5 O2( g) ¡ 3 CO2( g) + 4 H2O( g) ΔH° rxn = -2044 kJ

Indicate and explain the sign of ΔS_univ for each process. a. 2 H₂( g) + O₂( g) → 2 H₂O (l ) at 298 K.