Half-life of things

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I’ve been reading about HL, but I still don’t get why would you use it. So, if half life of coffee is 5h, how that info is relevant when we know that full life is 10 (roughly)? On top of that, how do you get the half-life of a material other than waiting to be completely ‘dead’ and say, ok full life is X, the half life is X/2.
Also, let’s take uranium which in Earth’s crust has a half-life of almost 4.5 billion years.. how did we get this number?

Thank you!

In: Chemistry

16 Answers

Anonymous 0 Comments

The half-life is always the same, no matter how much you start with.

An espresso has about 200mg of caffeine. The half life is 5 hours, which means that 5 hours later, you’ll have about 100mg of caffeine in your system. 5 hours after that, you’ll have 50mg. Another 5 hours later, you’ll have 25mg.

This means that if you drink two shots of espresso back to back, you’ll start out with 400mg, and 5 hours later, you’ll be down to 200mg.

Caffeine isn’t like the fuel in a car that depletes at fixed rate (assuming you’re running the engine in a consistent way). It’s not really possible to wait until it’s all gone, and it doesn’t really make sense to do that anyway.

With fuel in a car, whether the tank is full, half full, or only has a little bit of reserve left, it doesn’t change the power of the engine. But with caffeine, the power of the effect is related to how much you’ve taken. That 400mg double espresso is going to give you quite a kick, maybe even some jitters. When you only have 25mg left in your body, you’re not going to notice much of an effect any more.

So with a car, if you’re going for a road trip, you can fill the tank up all the way, and you’re good to go all day. But with coffee, there’s a big difference between starting the day with a double espresso versuses sipping chai latte throughout the day, even if it’s the same amount of caffeine overall. With the double espresso, you’ll get a big kick, which will taper off throughout the day, but sipping a lighter caffeine drink will maintain a more stable caffeine level.

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