View Full Version : Stoichiometry Nightmare!

12-16-2005, 03:54 PM
Hey can you help me solve problems dealing with stp and find the air? And doing a multistep conversion when i have to find the grams and do the process.:(

12-16-2005, 04:05 PM
What are the problems?:confused: :confused::eek: :confused: :eek: :eek: :mad: :)

12-17-2005, 06:48 AM
the problem is if i burned 4.0x10^24 molecules of methane (CH4) what mass of methane did i burn. it gives me the answer but i have to do the process of finding the answer. The answer is 110g but i dont know how they get it.

2.) A room with a volume of 4000 L conains how many molecules of air at STP? The answer is 178.6 molecules of air but how do u get the answer.

12-28-2005, 12:31 PM
1) for this, you have to first find the volume of 1 mole of methane by adding the molar mass of each of the elements in the formula (H=1 C=12.01) so CH4 = 12.01+4, so 1 mole or 6.02x10^23 particles of CH4 weighs 16.01 grams. after that, im not so sure. but i hoped that helped.:)

12-29-2005, 01:09 PM
Yes it did thank you very much.:) :)

01-04-2006, 10:56 AM
what is stoichiometry? Is it a type of math?

01-04-2006, 12:52 PM
no, it is a type of science dealing with moles(the unit, not the thing on your face). here is a sample question:

sodium reacts with oxygen to produce sodium oxide.
4Na(s) + O2(g) --> 2Na2O(s)

a) how many grams of Na20 are produced when 2.5 moles of Na react?
b)If you have 18g of Na, how many grams of O2 are required for a reaction?
c)How many grams of O2 are needed in a reaction that produces 75 grams of Na2O?

:confused: :eek: :confused:

As you can see, its hard!!

try to figure it out. ill post the anwsers soon

01-10-2006, 01:20 PM
come on, no guesses?

01-12-2006, 07:30 PM
before you get into that, how about you understand what a mole is...

A mole is a standard of measurement for elements, because saying I have one pound/gram of carbon is very inexact and not very useful. So the scientific community uses the term mole. If the atomic mass of an element is x amu, then one mole of that element is x grams.

01-15-2006, 10:17 AM
oh, and BTW, 1 mole is equal to 6.02 x 10^23. that's 602 000 000 000 000 000 000 000 000!!! that is also six hundred 2 trillion trillion!!!

01-15-2006, 10:36 AM
okay, there are few ways to define moles. One is the gram molecular forumla, which I previously mentioned. The gram molecular formula is the atomic weight of the compound or element in grams. The way Bman mentioned it, is by how many molecules are in a mole. If there is one mole of oxygen (O2), then there are 6.02 times 10 to the 23rd molecules of O2 in that mole. Since one oxygen has an atomic weight of 16 amu, then O2 has an atomic weight of 32 amu. 32 amu, in gram molecular formula, would equal 32 grams. So basically, 32 grams of O2 is the same as 6.2 times 10 to the 23rd molecules of O2, which is the same as one mole of O2.

The third way to define mole, but ONLY for gases. One mole of a gas (no matter what gas) takes up 22.4 Liters at STANDARD TEMPERATURE AND PRESSURE (commonly notated as STP). So one mole of O2 would also be 22.4 Liters of O2 at STP.

Hopefully, this has clarified or helped someone... :D