MCQ Collection
ECAT Chemistry MCQs
Practice ECAT Chemistry questions with answers and explanations.
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Correct Answer: D. Higher temperature increases rate
Explanation:
Higher temperature increases collision frequency and energetic collisions.
More particles exceed the activation-energy barrier.
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Correct Answer: A. It increases collision frequency and usually increases rate
Explanation:
More particles per volume collide more often.
The exact effect is described by the rate law.
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Correct Answer: B. It usually increases rate
Explanation:
More exposed particles are available for collision.
Powders often react faster than large pieces.
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Correct Answer: B. -125 kJ/mol
Explanation:
Heat release gives a negative enthalpy sign.
-250 kJ divided by 2 mol equals -125 kJ/mol.
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Correct Answer: B. An acid that ionizes only partially in water
Explanation:
Weak-acid solutions contain both ionized and unionized forms.
They establish an equilibrium in water.
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Correct Answer: C. 4180 J
Explanation:
Use q=mcΔT.
Q=100×4.18×10 = 4180 J.
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Correct Answer: C. Negative logarithm of hydrogen-ion activity or approximate concentration
Explanation:
For dilute solutions, pH≈-log[H+].
Lower pH generally means greater acidity.
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Correct Answer: D. 1.0 J/g·°C
Explanation:
Use c=q/(mΔT).
C=1000/(50×20)=1.0 J/g·°C.
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Correct Answer: D. Negative logarithm of hydroxide-ion concentration
Explanation:
For dilute aqueous solutions, pOH=-log[OH-].
At 25°C, pH+pOH≈14.
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Correct Answer: A. -40 kJ
Explanation:
Use ΔG=ΔH-TΔS.
ΔG=-100-300(-0.20)=-40 kJ.
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Correct Answer: B. A solution that resists large pH changes
Explanation:
Buffers contain a weak acid-base pair.
They consume added H+ or OH-.
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Correct Answer: B. -30 kJ
Explanation:
Use ΔG=50-400(0.20).
ΔG=50-80=-30 kJ.
