Chemical Thermodynamics - SS2 Chemistry Past Questions and Answers - page 2
Which of the following statements is true about the Gibbs free energy (ΔG) of a reaction?
ΔG < 0 indicates a spontaneous reaction.
ΔG > 0 indicates a spontaneous reaction.
ΔG = 0 indicates a non-spontaneous reaction.
ΔG can only be determined experimentally.
The relationship between enthalpy change (ΔH), entropy change (ΔS), and Gibbs free energy change (ΔG) is given by:
ΔG = ΔH - TΔS
ΔG = ΔH + TΔS
ΔG = ΔH/T - ΔS
ΔG = ΔH/T + ΔS
For a spontaneous process at constant temperature and pressure, which of the following conditions must be satisfied?
ΔH < 0 and ΔS < 0
ΔH > 0 and ΔS > 0
ΔH > 0 and ΔS < 0
ΔH < 0 and ΔS > 0
The standard Gibbs free energy change (ΔG°) of a reaction can be calculated using the equation:
ΔG° = ΔH° - TΔS°
ΔG° = ΔH° + TΔS°
ΔG° = ΔH°/T - ΔS°
ΔG° = ΔH°/T + ΔS°
Which of the following factors can affect the spontaneity of a reaction?
Temperature only
Pressure only
Concentration of reactants only
Temperature, pressure, and concentration of reactants
The Third Law of Thermodynamics states that:
The total energy of the universe is constant.
Energy can neither be created nor destroyed.
The entropy of a perfect crystal at absolute zero is zero.
The entropy of a system always increases.
Calculate the change in Enthalpy (ΔH) for a reaction given the following information:
Reaction: 2H2(g) + O2(g) → 2H2O(g)
ΔHf° (H2O(g)): -241.8 kJ/mol
ΔHf° (H2(g)): 0 kJ/mol
ΔHf° (O2(g)): 0 kJ/mol
ΔH = 2 × ΔHf° (H2O(g)) - [2 × ΔHf° (H2(g)) + ΔHf° (O2(g))]
= 2 × (-241.8 kJ/mol) - [2 × 0 kJ/mol + 0 kJ/mol]
= -483.6 kJ/mol
Calculate the change in Entropy (ΔS) for a reaction given the following information:
Reaction: N2(g) + 3H2(g) → 2NH3(g)
ΔS° (N2(g)): 191.5 J/(mol·K)
ΔS° (H2(g)): 130.6 J/(mol·K)
ΔS° (NH3(g)): 192.5 J/(mol·K)
ΔS = 2 × ΔS° (NH3(g)) - [ΔS° (N2(g)) + 3 × ΔS° (H2(g))]
= 2 × (192.5 J/(mol·K)) - [191.5 J/(mol·K) + 3 × 130.6 J/(mol·K)]
= 71.7 J/(mol·K)
Calculate the Gibbs Free Energy (ΔG) for a reaction given the following information:
Reaction: 2H2O(g) → 2H2(g) + O2(g)
ΔGf° (H2O(g)): -237.2 kJ/mol
ΔGf° (H2(g)): 0 kJ/mol
ΔGf° (O2(g)): 0 kJ/mol
ΔG = 2 × ΔGf° (H2(g)) + ΔGf° (O2(g)) - 2 × ΔGf° (H2O(g))
= 2 × 0 kJ/mol + 0 kJ/mol - 2 × (-237.2 kJ/mol)
= 474.4 kJ/mol
Please note that the ΔHf°, ΔS°, and ΔGf° values used in these calculations represent the standard enthalpy, entropy, and Gibbs free energy of formation, respectively, at 25°C (298 K) and 1 atm pressure.
Which of the following statements is true about a spontaneous process?
It always occurs quickly.
It requires an input of energy.
It occurs without any external intervention.
It always leads to an increase in entropy