Half lives

Where are half life equations derived from?

Integrated rate laws

For which order reaction is the half life constant?

a first order reaction has a constant half life

For which order reaction is the lifetime constant?

First order has a constant lifetime

What is the half life equation for a first order reaction?

t1/2= 0.693/k

For which order reaction does the half life NOT DEPEND on initial concentration?

First order reaction

What does K dictate? in half life?

K dictates how fast a reaction will decay

What does K represent in half life?

“K” is a proportionality factor that quantifies the speed and probability of a chemical reaction or radioactive decay.

What is “K” called?

The rate constant

Rate constant “K” and half-life have an inverse relationship. This means that a larger K value means:

A shorter half life

What would a high k value represent in half life?

fast decay = shorter half life

You can use the exponential decay formula for half life when a substance decreases at a rate proportional to its current amount. Which order reaction would this formula be used for ONLY?

A first order reaction

True or false: You can use the exponential decay formula ONLY for a first order reaction

True

What does “Constant Half-Life” mean?

The time it takes to lose half the substance is the same.

In a graph, how does the reactant concentration decay like in a zero order reaction?

It decays linearly

In a graph, how does the reactant concentration decay like in a second order reaction?

It decays reciprocally

Why can we use the exponential decay formula for a first order reaction ONLY?

You can use the exponential decay formula for a first-order reaction because the reactant concentration decays exponentially

What do we need to know to determine the rate constant? t 1/2?

The reaction order, the rate constant “K”, and sometimes the Initial concentration [Ao]

What kind of relationship do k and the half life have?

Inverse or opposite relation