Half life calculations

[Alyssa Cheung-2J]

For half life in first order reactions, can we divide the first order equation and get the correct half life? can the half life be applied to second or third order reactions?

[Nicole Coulter]

Yes, when given k (rate constant) you can use the half-life equation for first-order reaction and get the half life from 0.693/k. There are also half life equations for 2nd order (we have the equation for and learned), and 3rd order (we did not learn)
2nd order equations depend on a given concentration so you cannot determine it just when given rate constant, k, like in the first-order equation.

[BB Dis 1H]

Yes! For a first order reaction you can use the equation t1/2 = 0.693 / k to solve for either the half life or k, depending on what information is given. We also know that the half life equation for zero order is t1/2 = [A]0 / 2k and the half life equation for second order is t1/2 = 1/k[A]0. So, for zero and second order you also need the starting concentration.

[405981594]

yes you can use K to determine the half-life through the equation. Other orders have other half-times.