Thermodynamics

Gibbs Free Energy [G] represents the energy available to do work in a system. Which of the following is the correct definition of Gibbs Free Energy?

• It is the total energy of a system, including kinetic and potential energy.

• It is the energy available to do work and is defined as G=H−TS, where H is enthalpy, T is temperature, and S is entropy.

• It is the energy required to start a chemical reaction.

• It is the measure of heat energy in a system at constant pressure.

Which equation correctly describes the relationship between Gibbs Free Energy (ΔG) and the equilibrium constant (K)?

• ΔG = RT ln K

• ΔG = − RT ln K

• ΔG = K RT

• ΔG = −K RT ln K

Use of Equilibrium Constant - You are given 50 g of gypsum (CaSO₄⋅2H₂O) and placed in a 1.00 L solution at 25°C. The following equation represents the dissociation of gypsum in water:

CaSO₄​ (s) ⋅ 2H₂O (s) ⇌ Ca²⁺ (aq) + SO₄^2−​ (aq) + ⋅2 H₂O (l)

The solubility product constant (K_s​) for calcium sulfate at 25°C is 2.4×10⁻⁵ and the molar mass of CaSO4⋅2H2O is 146.14 g/mol.

What is the concentration of Ca²⁺ in the solution at equilibrium?

• 3.5×10⁻³M

• 1.7×10⁻³M

• 4.8×10⁻³M

• 2.4×10⁻⁴M

How does temperature affect the equilibrium constant (K) of a reaction according to the Van’t Hoff equation?

(d ln K​)/(dT) = (ΔH∘​/RT²)

• K increases for exothermic reactions as temperature increases.

• K increases for endothermic reactions as temperature increases.

• K is not affected by temperature.

• K decreases for exothermic reactions as temperature increases.

Which of the following statements correctly describes the pH of an acidic solution?

• The concentration of hydrogen ions is less than the concentration of hydroxide ions, and the pH is greater than 7

• The concentration of hydrogen ions is greater than the concentration of hydroxide ions, and the pH is less than 7.

• The concentration of hydrogen ions equals the concentration of hydroxide ions, and the pH is 7.
  

• The concentration of hydrogen ions is greater than the concentration of hydroxide ions, and the pH is greater than 7.

A commercial hydrochloric acid (HCl) solution is purchased as a 36 weight percent solution. The specific gravity of the solution is 1.18. Calculate the concentration of HCl in mg/L, molarity, and normality of the solution. The molecular weight of HCl is 36.46 g/mol.

• HCl concentration = 3.8 x 10⁵ mg/L, molarity = 10.5 M, normality = 10.5 N

• HCl concentration = 5.1 x 10⁵ mg/L, molarity = 14.0 M, normality = 11.65 N

• HCl concentration = 4.25 x 10⁵ mg/L, molarity = 11.65 M, normality = 11.65 N

• HCl concentration = 2.95 x 10⁵ mg/L, molarity = 9.8 M, normality = 9.8 N

If 50 mg of HCl (MW 36.46) is added to water, bringing the final volume to 1 L, what is the final pH?

• pH = 2.86

• pH = 1.02

• pH = 3.32

• pH = 0.72

Which of the following best describes the process of volatilization?

• A solid turning directly into a gas.

• A gas turning into a liquid.

• A gas turning into a solid.

• A liquid turning into a gas.

The Henry’s law constant for the transfer of carbon dioxide from air into water is 3.30 x 10-2 mole/L-atm at 20°C. What is the dimensionless KH for the transfer of carbon dioxide from water into air at 20°C?

KH= [K_H × ​(L-atm/mole)] / [R×T(K)]​

R = 0.08205 L-atm/mole·K (gas constant)

• 1.37 × 10⁻³

• 2.15 × 10⁻³

• 3.52 × 10⁻³

• 4.95 × 10⁻³