12: A first-order reaction is 40% complete at the end of 50. minutes, what is th

Question

12: A first-order reaction is 40% complete at the end of 50. minutes, what is the value of the rate constant (in min-)? A) 1.8 x 10-2 B) 1.0x 10 C) 1.2 x 10 D) 8.0 x 10- E) none of these 13. When ethyl chloride, CH,CH.CI, is dissolved in 1.0 M NaOH, it is converted into ethanol, CH,CH OH, by the reaction CH,CH2Cl + OH. CH,CH2011 + Cl. At 25 C the reaction is first order in CH CH,CI, and the rate constant is 1.0 x 10 s. If the activation parameters are A -3.4x 10 and E- 100.0 kJ/mol, what will the rate constant be at 40 C? A) 1.7 x 10 B) 6.9x 10- s C) 5.0 x 103 s D) 2.0x 103 s-1 E) 5.0x 10"s 14. Which of the following statements concerning equilibrium is not true? A) Equilibrium in molecular systems is dynamic, with two opposing processes balancing one another B) The value of the equilibrium constant for a given reaction mixture is the same regardless of the direction from which equilibrium is attained. C) A system moves spontaneously toward a state of equilibrium. D) The equilibrium constant is independent of temperature. 15. Apply the law of mass action to determine the equilibrium expression for C)

Explanation / Answer

12) Solution-

For a first-order reaction

ln( [A] / [A] ) = - k · t
[A] =concentration at time t
[A] =initial concentration t=0

From the question, we found the reaction is 40% complete 60% of reactant A is still there.

Therefore [A] / [A] = 0.6
=>
k = - ln( [A] / [A] ) / t
= - ln(0.6)/50min
= 0.0102min^-1

=1.0*10^-2 min^-1

So option B is correct

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