CHEM 210 – General & Organic Chemistry | Exam 3 | Comprehensive Final Assessment | 100% Pass Guaranteed | Graded A+

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CHEM 210 – General & Organic Chemistry | Exam 3 |
Comprehensive Final Assessment | 100% Pass Guaranteed |
Graded A+



1. Which of the following statements correctly describes the relationship between ΔG°, ΔH°,


and ΔS° for a reaction that is spontaneous at all temperatures?


A. ΔH° < 0 and ΔS° < 0


B. ΔH° > 0 and ΔS° > 0


C. ΔH° < 0 and ΔS° > 0


D. ΔH° > 0 and ΔS° < 0


☑ Correct Answer: C


☑ Explanation: The Gibbs free energy equation is ΔG° = ΔH° - TΔS°. For a reaction to be

spontaneous at all temperatures, ΔG° must always be negative. This requires ΔH° to be negative


(exothermic) and ΔS° to be positive (increase in entropy), because the -TΔS° term will always be


negative, and the ΔH° term will also be negative. Option A would be spontaneous only at low


temperatures. Option B would be spontaneous only at high temperatures. Option D would be


nonspontaneous at all temperatures.

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2. The equilibrium constant Kp for the reaction 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) is 2.5 × 10⁴ at 25°C.


What is the value of Kc for this reaction at the same temperature? (R = 0.0821


L·atm·mol⁻¹·K⁻¹)


A. 2.5 × 10⁴


B. 1.0 × 10⁶


C. 4.2 × 10²


D. 6.1 × 10⁵


☑ Correct Answer: D


☑ Explanation: The relationship between Kp and Kc is Kp = Kc(RT)^Δn, where Δn = moles of

gas products - moles of gas reactants. For this reaction, Δn = 2 - (2 + 1) = -1. Therefore, Kp =


Kc(RT)^(-1). Rearranging: Kc = Kp(RT) = (2.5 × 10⁴)(0.0821 × 298) = (2.5 × 10⁴)(24.5) = 6.125 ×


10⁵, approximately 6.1 × 10⁵. Option A is incorrect because it ignores the Δn factor. Option B and


C are incorrect calculations.




3. Which of the following is the correct equilibrium expression for the dissolution of calcium


fluoride (CaF₂) in water?


A. Ksp = [Ca²⁺][F⁻]²

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B. Ksp = [Ca²⁺][F⁻]


C. Ksp = [Ca²⁺][2F⁻]²


D. Ksp = [Ca²⁺]²[F⁻]


☑ Correct Answer: A


☑ Explanation: The dissolution of CaF₂ is represented by the equation: CaF₂(s) ⇌ Ca²⁺(aq)

+ 2F⁻(aq). The solubility product expression is the product of the concentrations of the ions, each


raised to the power of its stoichiometric coefficient. The concentration of the solid is not


included. Therefore, Ksp = [Ca²⁺][F⁻]². Option B has the incorrect exponent. Option C incorrectly


places the coefficient in the brackets. Option D has the ions reversed.




4. The pH of a solution is 4.5. What is the pOH of this solution at 25°C?


A. 4.5


B. 9.5


C. 10.5


D. 7.0


☑ Correct Answer: B

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☑ Explanation: At 25°C, pH + pOH = 14. Therefore, pOH = 14 - pH = 14 - 4.5 = 9.5. Option A

is the pH. Option C is incorrect. Option D is the pH of a neutral solution.




5. The Arrhenius equation relates the rate constant (k) to temperature (T). Which of the


following correctly describes the effect of a catalyst on the Arrhenius parameters?


A. A catalyst increases the activation energy (Ea)


B. A catalyst decreases the activation energy (Ea) without changing the frequency factor (A)


C. A catalyst decreases the activation energy (Ea) and changes the frequency factor (A)


D. A catalyst changes the temperature dependence of the rate constant


☑ Correct Answer: C


☑ Explanation: A catalyst provides an alternative reaction pathway with a lower

activation energy (Ea), which increases the rate constant. Catalysts can also affect the frequency


factor (A) by altering the orientation or nature of the reaction. However, the primary effect is


lowering Ea. Option A is incorrect; catalysts lower Ea. Option B is partly correct but incomplete


because catalysts can also change A. Option D is incorrect; catalysts do not change the


fundamental temperature dependence.