General Science MCQ – 24 (Chemistry)

chemistry, physics, biology

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General Science MCQs including Physics, Chemistry, Biology. This help is General Eligibility Test like Entrance Exam, Sainik School, NDA, Army, All India Competitive exam, and All HP Exams. You can also play our weekly quiz and download all quizzes PDF as well.

1. Which of the following substance has the lowest standard molar entropy (So) at 25o C?
(A) CH3OH(l)
(B) CO(g)
(C) MgO(s)
(D) H2O(l)

2. When crystalline solid barium hydroxide octahydrate and crystalline solid ammonium nitrate are mixed in a beaker at room temperature, a spontaneous occurs. The temperature of the beaker contents rapidly falls to below 0o use this information to decide whether the reaction is exothermic or endothermic and what the sign of ΔH and ΔS are?
(A) Endothermic; ΔH > 0; ΔS > 0
(B) Endothermic; ΔH < 0; ΔS > 0
(C) Endothermic; ΔH < 0; ΔS < 0
(D) Endothermic; ΔH > 0; ΔS < 0

3. Sodium carbonate can be made by heating sodium hydrogen carbonate:
2NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g)
For this reaction, ΔH° = 128.9 kJ and ΔS° = 321 J/K. At approximately what temperature will K = 1?

(A) 401.6 K
(B) 401.6o K
(C) 402.6 C
(D) 33.1 K

4. For the overall hypothetical reaction A + 5B → 4C, the rate of appearance of C given by Δ[C]/Δt is the same as?
(A) -(5/4)(Δ[B]/Δt)
(B) Δ[A]/Δt
(C) -(4/5)(Δ[B]/Δt)
(D) None of these

5. The initial rate of the reaction
PCl5→ PCl3 + Cl2
is increased a factor of four when the concentration of PCl5 is doubled. Therefore, the rate?

(A) Is second order with respect to PCI3
(B) Is first order with respect to PCI3
(C) Is second order with respect to PCI5
(D) Is first order with respect to PCI5

6. Consider the reaction A -> products. Which of the following plots is consistent with a zero-order reaction?
(A) In [A] plotted against time gives a straight line of negative slope
(B) [A] plotted against time gives a horizontal, straight line.
(C) [A] plotted against time gives a curved line of negative slope, decreasing in magnitude as time increase
(D) [A] plotted against time gives a straight line of negative slope

7. The rate constant of a first-order reaction is 3.68 x 10-2 s-1 at 150o C, and the activation energy is 71 kj/mol. What is the value of the rate constant at 170o C?
(A) 9.2 x 10-2 s-1
(B) 9.5 x 11-2 s-1
(C) 3.7 x 10-2 s-1
(D) 2.49 s-1

8. The reaction
3ClO(aq) → ClO3(aq)
+ 2Cl(aq) has been proposed to occur by the following mechanism.
ClO(aq) + ClO( aq)→ ClO2(aq) + Cl( aq) (slow)
ClO2(aq) + ClO(aq) → ClO3(aq) + Cl (aq) (fast)
Which rate law is consistent with this mechanism?
(A) Rate = k[CI][CIO]2
(B) Rate = k[CIO]3
(C) Rate = k[CIO]
(D) Rate = k[ClO]2

9. A catalyst speeds up a reaction by?
(A) Providing a new reaction pathway for molecules
(B) Increasing the number of high-energy molecules
(C) Increasing the temperature of the molecules in the reaction
(D) Increasing the activation energy for the reaction

10. Consider the following gas-phase equilibrium:
H2(g) + I2(g) ↔ 2HI(g) At a certain temperature, the equilibrium constant Kc is 4.0. Starting with equimolar quantities of H2 and I2 and no HI, when equilibrium was established, 0.20 moles of HI was present. How much H2 was used to start the reaction?
(A) 4.0 mil
(B) 0.23 mol
(C) 0.20 mol
(D) 0.10 mol

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