Question 7 in the C of Cu Lab, I tried to purposely to confuse you with what is called a RED HERRING.
A red herring is a distraction, a shiny object to catch your attention from what is important to pay attention to. It’s designed to confuse you, and in someways it’s a trick. But it was my hope to help you focus more on writing a formula to figure out a chem math problem. Don’t just do what you want, do what is right.
It reads…
If you took that same amount of energy, 125,200 Joules, how much water could you vaporize into steam at 373 Kelvin?
Most of you got fooled by the “373 Kelvin”. Let’s discuss why you got such an easy question wrong.
You know that vaporization of water happens at 373 Kelvin, and since the number is RIGHT THERE in the question, you think that you somehow, and for some reason you can’t quite explain, that you have to stick it into your math. For all the wrong reasons, you squish that 373 K into the math and hope for the best.
It’s only there to trick you. You know how to do the math, you know the formula, trust that the math will turn out okay. Think before you leap into messy math. Think: have we stuck in a temperature before? Does the necessary formula even ASK FOR a temperature (no).
If you just write the formula (for vaporization of water)
q = mHV
and put the numbers where they belong, the math is easy. Let’s try that now.
q = mHV
125,200 J = (m)(2260 J/g)
m = 55.40 grams of water.
Not too hard really.
There is just no place for the 373 Kelvin really either, except your head. Use the right formulas, and put your numbers in the right place.
A red herring is something stuck into a problem that just is there to distract you away from doing it correctly.
