Half-life for first and second order reactions: A certain first-order reaction (

Question

Half-life for first and second order reactions: A certain first-order reaction (A--products) has a rateconstant of 9.90*10-3 s-1 at 45oC. How manyminutes does it take for th concentration of the reactant [A], todrop to 6.25% of the original concentration? Answer numerically inminutes. A certain second-order reaction (B--product) has a rateconstant of 1.70*10-3 m-1*s-1 at 270C and aninitial half-life of 254s. What is the concentration of thereactant B after one half-life? Express the molar concentrationnumerically. Half-life for first and second order reactions: A certain first-order reaction (A--products) has a rateconstant of 9.90*10-3 s-1 at 45oC. How manyminutes does it take for th concentration of the reactant [A], todrop to 6.25% of the original concentration? Answer numerically inminutes. A certain second-order reaction (B--product) has a rateconstant of 1.70*10-3 m-1*s-1 at 270C and aninitial half-life of 254s. What is the concentration of thereactant B after one half-life? Express the molar concentrationnumerically.

Explanation / Answer

First order reaction ln(A0/A) = kt A = 0.0625*A0 ln(1/0.0625) = 9.9e-3 *t t = 279.213366 seconds t = 4.65 minutes ============ A certain second-order reaction (B--product) has a rate constant of1.70*10-3 m-1*s-1 at 270C and an initialhalf-life of 254s. What is the concentration of the reactant Bafter one half-life? Express the molar concentrationnumerically. Second order 1/[A] - 1/[A]0 = kt [A] = 0.5*[A]0   at t = 254 seconds 1/0.5[A]0 - 1/[A]0 = 1/[A]0 = kt = 1.7e-3 *254 = 0.4318 [A]0 = 1/0.4318 = 2.32 M

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