Q. If the enthalpy change for a reaction is +75 kJ for 2 moles, what is the enthalpy change per mole?
A.37.5 kJ
B.75 kJ
C.150 kJ
D.25 kJ
Solution
ΔH per mole = 75 kJ / 2 mol = 37.5 kJ/mol.
Correct Answer: A — 37.5 kJ
Q. If the enthalpy change for a reaction is -500 kJ for 5 moles, what is the enthalpy change for 1 mole?
A.100 kJ
B.500 kJ
C.200 kJ
D.50 kJ
Solution
ΔH for 1 mole = -500 kJ / 5 mol = -100 kJ/mol.
Correct Answer: C — 200 kJ
Q. If the equilibrium constant Kc for the reaction A + B ⇌ C is 4 at 25°C, what will be the value of Kc if the concentration of A is doubled?
A.1
B.2
C.4
D.8
Solution
Doubling the concentration of A will shift the equilibrium to the right, but Kc remains constant at 4.
Correct Answer: C — 4
Q. If the equilibrium constant Kc for the reaction A ⇌ B is 0.1, what can be inferred about the concentrations of A and B at equilibrium?
A.A > B
B.A < B
C.A = B
D.Cannot be determined
Solution
Since Kc < 1, it indicates that at equilibrium, the concentration of A is greater than that of B.
Correct Answer: A — A > B
Q. If the equilibrium constant Kp for the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g) is 25 at a certain temperature, what is Kp if the volume of the system is halved?
A.12.5
B.25
C.50
D.100
Solution
Kp is independent of volume changes; it remains 25.
Correct Answer: C — 50
Q. If the half-life of a first-order reaction is 10 minutes, what is the rate constant?
A.0.0692 min^-1
B.0.1 min^-1
C.0.693 min^-1
D.0.5 min^-1
Solution
For a first-order reaction, the half-life (t1/2) is given by t1/2 = 0.693/k. Rearranging gives k = 0.693/t1/2 = 0.693/10 min = 0.0692 min^-1.
Correct Answer: A — 0.0692 min^-1
Q. If the rate constant of a reaction doubles when the temperature increases by 10°C, what is the approximate activation energy (Ea) of the reaction?
A.20 kJ/mol
B.40 kJ/mol
C.60 kJ/mol
D.80 kJ/mol
Solution
Using the Arrhenius equation, a doubling of the rate constant corresponds to an activation energy of approximately 40 kJ/mol for a 10°C increase.
Correct Answer: B — 40 kJ/mol
Q. If the rate of a reaction doubles when the concentration of reactant A is tripled, what is the order of the reaction with respect to A?
A.0
B.1
C.2
D.3
Solution
If doubling the rate occurs when tripling the concentration, the reaction is first order with respect to A, as rate ∝ [A]^n implies 2 = 3^n.
Correct Answer: B — 1
Q. If the rate of a reaction doubles when the temperature increases from 300 K to 310 K, what is the approximate activation energy (Ea) in kJ/mol?
A.20.8
B.40.8
C.60.8
D.80.8
Solution
Using the Arrhenius equation and the two-point form, Ea can be estimated as Ea ≈ 2.303RT²(Δlnk/Δ(1/T)). With R = 8.314 J/(mol·K), Ea ≈ 40.8 kJ/mol.
Correct Answer: B — 40.8
Q. If the rate of a reaction is 0.05 M/s when the concentration of reactant A is 0.1 M, what is the rate constant k for a first-order reaction?
A.0.5 s^-1
B.1.0 s^-1
C.0.05 s^-1
D.0.1 s^-1
Solution
For a first-order reaction, rate = k[A]. Thus, k = rate / [A] = 0.05 M/s / 0.1 M = 0.5 s^-1.
Correct Answer: A — 0.5 s^-1
Q. If the rate of a reaction is proportional to the square of the concentration of reactant A, what is the rate law?
A.rate = k[A]
B.rate = k[A]^2
C.rate = k[A]^3
D.rate = k[A]^0
Solution
If the rate is proportional to the square of the concentration of A, the rate law is rate = k[A]^2.
Correct Answer: B — rate = k[A]^2
Q. If the temperature of an exothermic reaction at equilibrium is increased, what will be the effect on the equilibrium position?
A.Shifts to the right
B.Shifts to the left
C.No effect
D.Reaction rate increases
Solution
For an exothermic reaction, increasing the temperature shifts the equilibrium to the left, favoring the reactants, as the system tries to absorb the added heat.
Correct Answer: B — Shifts to the left
Q. If the temperature of an exothermic reaction at equilibrium is increased, what will happen to the equilibrium position?
A.Shift to the right
B.Shift to the left
C.No change
D.Reaction rate increases
Solution
For an exothermic reaction, increasing the temperature shifts the equilibrium to the left, favoring the reactants, as the system tries to absorb the added heat.
Correct Answer: B — Shift to the left
Q. If the temperature of an exothermic reaction is increased, what is the expected effect on the equilibrium?
A.Shifts to the right
B.Shifts to the left
C.No effect
D.Reaction rate increases
Solution
For an exothermic reaction, increasing the temperature shifts the equilibrium to the left, favoring the reactants, as the system tries to absorb the added heat.
Correct Answer: B — Shifts to the left
Q. If the temperature of an exothermic reaction is increased, what will happen to the equilibrium?
A.Shift to the right
B.Shift to the left
C.No change
D.Reaction rate increases
Solution
For an exothermic reaction, increasing the temperature shifts the equilibrium to the left, favoring the reactants, as the system tries to absorb the added heat.
Correct Answer: B — Shift to the left
Q. In a back titration, what is the first step?
A.Add excess titrant to the analyte
B.Measure the pH of the solution
C.Dilute the analyte solution
D.Add a color indicator
Solution
In a back titration, the first step is to add an excess of titrant to the analyte, followed by titrating the unreacted titrant.
Correct Answer: A — Add excess titrant to the analyte
Q. In a calorimetry experiment, if 50 g of water is heated from 25 °C to 75 °C, what is the heat absorbed (q) assuming specific heat capacity of water is 4.18 J/g°C?
A.1045 J
B.2090 J
C.1250 J
D.500 J
Solution
q = mcΔT = 50 g × 4.18 J/g°C × (75-25)°C = 1045 J.
Correct Answer: B — 2090 J
Q. In a calorimetry experiment, what does a negative q value indicate?
A.Heat is absorbed by the system.
B.Heat is released by the system.
C.No heat exchange occurs.
D.The reaction is at equilibrium.
Solution
A negative q value indicates that heat is released by the system, signifying an exothermic process.
Correct Answer: B — Heat is released by the system.
Q. In a calorimetry experiment, what does a negative ΔH indicate?
A.The reaction is endothermic.
B.The reaction is exothermic.
C.No heat exchange occurs.
D.The system is at equilibrium.
Solution
A negative ΔH indicates that the reaction releases heat to the surroundings, classifying it as exothermic.
Correct Answer: B — The reaction is exothermic.
Q. In a calorimetry experiment, what does a positive q value indicate?
A.Heat is released by the system
B.Heat is absorbed by the system
C.No heat exchange occurs
D.The system is at equilibrium
Solution
A positive q value indicates that the system absorbs heat from the surroundings.
Correct Answer: B — Heat is absorbed by the system
Q. In a chemical reaction, if the enthalpy change (ΔH) is negative, what does this indicate?
A.The reaction is endothermic
B.The reaction is exothermic
C.The reaction is at equilibrium
D.The reaction requires energy input
Solution
A negative ΔH indicates that the reaction releases heat to the surroundings, classifying it as exothermic.
Correct Answer: B — The reaction is exothermic
Q. In a closed container, if the temperature of a gas is increased, what happens to its pressure?
A.Pressure decreases
B.Pressure increases
C.Pressure remains constant
D.Pressure fluctuates
Solution
According to Gay-Lussac's Law, at constant volume, the pressure of a gas is directly proportional to its temperature in Kelvin.
Correct Answer: B — Pressure increases
Q. In a closed container, if the temperature of a gas is increased, what happens to the pressure if the volume remains constant?
A.Pressure decreases
B.Pressure remains constant
C.Pressure increases
D.Pressure fluctuates
Solution
According to Gay-Lussac's Law, pressure is directly proportional to temperature at constant volume (P/T = k).
Correct Answer: C — Pressure increases
Q. In a closed system, if 100 J of heat is added to a gas and it does 40 J of work, what is the change in internal energy (ΔU) according to the first law of thermodynamics?
A.60 J
B.40 J
C.100 J
D.140 J
Solution
ΔU = Q - W = 100 J - 40 J = 60 J.
Correct Answer: A — 60 J
Q. In a closed system, if the internal energy of the system increases, what can be said about the enthalpy?
A.Enthalpy decreases
B.Enthalpy increases
C.Enthalpy remains constant
D.Enthalpy is independent of internal energy
Solution
If the internal energy increases in a closed system, the enthalpy also increases, as ΔH = ΔU + PΔV.
Correct Answer: B — Enthalpy increases
Q. In a closed system, if the volume of a gas is halved while the temperature remains constant, what happens to the pressure?
A.It doubles
B.It halves
C.It remains the same
D.It quadruples
Solution
According to Boyle's Law, if the volume is halved, the pressure will double (P1V1 = P2V2).
Correct Answer: A — It doubles
Q. In a closed system, what happens to the pressure of a gas if its volume is halved at constant temperature?
A.Pressure doubles
B.Pressure halves
C.Pressure remains the same
D.Pressure quadruples
Solution
According to Boyle's Law, if the volume is halved, the pressure will double (P1V1 = P2V2).
Correct Answer: A — Pressure doubles
Q. In a concentration cell, if the concentration of the anode is 0.1 M and the cathode is 1 M, what is the cell potential at 25°C?
A.0.059 V
B.0.118 V
C.0.059 log(10)
D.0.118 log(10)
Solution
E = (0.059 V/n) * log([Cathode]/[Anode]) = (0.059 V/2) * log(1/0.1) = 0.059 V * 1 = 0.059 V.
Correct Answer: B — 0.118 V
Q. In a concentration cell, the cell potential is dependent on:
A.Temperature only
B.Concentration differences
C.Electrode material
D.Surface area of electrodes
Solution
In a concentration cell, the cell potential is dependent on the concentration differences of the reactants.
Correct Answer: B — Concentration differences
Q. In a constant pressure process, how is the work done by the system related to the change in enthalpy?
A.W = ΔH
B.W = -ΔH
C.W = ΔH + PΔV
D.W = ΔH - PΔV
Solution
For a constant pressure process, the work done by the system is related to the change in enthalpy by the equation ΔH = Q + PΔV, where Q is the heat added.
