Molar ǝɯnןoʌ of a Gas

Hello to our fellow blog readers! Happy new year to everyone! Have you been practicing some chemistry questions during the holiday?
If you haven't, Mr.(or Miss) PinchofKCN will be very disappointed. Today we're going to talk about molar volume of a gas.
I'm sure that you must be very excited about this, because everyone wants to do as much chemistry as possible before 2012 ends.

So here's a simple yet important question to get your brain work'in before our lesson:
『What is a gas?』
No, you don't invite gases to your birthday party, and you absolutely do not want to gas the age of a woman.
A gas is a state of matter that has the lowest density of all three classic states (liquid, solid, gas). A gaseous matter is made up of atoms or molecules that can move freely under room temperature. When gases like carbon and oxygen are heated sufficiently, combustion will happen. On the other hand, when CO2 is cooled, it'll condense into water vapour(liquid).
If  you would like a recap on the three states of matter, visit our past post here.

Since gas will expand when heated and contract when cooled, their volume changed at the blink of an eye. As a result, we have to understand the STP in order to calculate its volume. I know there must be a blank look on your face, and you should be wondering what in the world does STP stand for.
STP, or Standard Temperature and Pressure, is a set of data that allow scientists to compare their measurements to the gas's properties under a temperature of 0℃.
There isn't a universally accepted STP value, but the most widely accepted one is: 0 °C (32 °F or 273 K) and 1 atm.

Now, I believe everyone's clear on the idea of STP, right? So why don't we start doing some math together?

Double Dare time:

Calculate the volume occupied by 5.8g of carbon at STP.

Step1: Memorize the magic formula
One mole of gas will occupy 22.4 litre of gas.

1 mole of gas

22.4 L of gas

Step2: Calculate the mass of carbon

5.8g x 1mole  = 0.483 moles
       12.0 g


Step3: Use the magic formula!!!

Molar Volume= 22.4 L x 0.483moles = 10.8192 L
              1 mol


Step4: Sig figs

Now look at the question again. It asks for 2 sig figs, so we should round the answer up to 11L.

Final answer: Volume occupied by 5.8g of carbon at STP= 11L.


See? You've just calculated the volume of a gas in 4 steps!!! (2 steps, actually. Excluding memorization AND sig figs.) Don't you think it is as easy as blowing a bubble with gum? Now I'll wish you a good luck because there'll be a chapter 4 test on next Thursday. Remember to re-read all of our blog posts for Ch.4 and I'll promise you an A+! :)