AP Chemistry 2.4 Chemical Reaction Rates
Time to calculate some half-life. And no, you can't only half-pay attention.
|AP Chemistry||Chemical Reaction Rates|
Chemical and Physical Properties from Structure and Arrangement
|Test Prep||AP Chemistry|
What is the rate constant for a first-order reaction that has a half-life of 56.0 seconds?
And here are your potential answers:
So what is “half-life,” aside from the portion of your time you spend on Netflix? [Woman with feet up watching TV]
For the sake of this problem, “half-life” is the amount of time it takes for something
to decrease to half its initial value. As the problem tells us, in chemistry, “half-life”
often means how long it takes for half of a radioactive sample to decay, but it can [Sample decays and clock ticks]
also refer to how long it takes for half of some species to be consumed in a regular chemical
reaction. In this problem, we know that some species [Woman zaps magic stick to a man on stage and he disappears]
is disappearing following a first-order rate law, and half of it is gone after 56.0 seconds.
To find the rate constant, we have to remember the equation for half-life: [Girl using calculator]
t½ = 0.693/k, where k is the first-order rate constant.
If you don’t remember this equation, you can figure it out by starting with the rate
law and solving a first order ordinary differential equation.
That is, if you want to make life way harder for yourself. [Boy studying at his desk]
Might just want to take the plunge and memorize. So, we need to take this equation and plug
in the value of the half-life, t½ or half-life= 56.0 seconds. Solving
for k, we find that the rate constant equals 0.0124 per second.
So that means that A is the correct answer. Now quick, head over to CarbonDating.com before [Scientist using tablet]
you have your half-life – we mean mid-life – crisis.