How can I effectively balance chemical equations for an upcoming exam?

[kchan]

Okay, this is a bit stupid, but I have an exam tommorrow, and I have no idea how to balance chemical equations. (A bit late for studying, I know) but if anyone can help me, that'd be great. I just want to know how to balance it, and why. And any rules and tips would be great.

 

[thunderfvck]

SO easy.
Just balance the equation. You want it balanced in the sense that you have the same number of elements on both sides. When you have a number in front (a coefficient) of any series of letters, like 2H2O, that means you have 2*2 = 4 H's and 2*1 = 2 O's. So it's up to you to balance the equation by putting the right coefficients in front of the letters. BTW the letters actually symbolize chemicals but you probably knew that.

ie. 2H2 + O2 --> 2H2O


H's (on left) --> 2H2 --> 2*2 = 4 <-- 2H2O <-- (on right) H's
O's (on left) --> O2 --> 2*1 = 2 <-- 2H2O <-- (on right) O's

So now you understand what you actually HAVE to do, but now you need a method for doing it. I'll show you how I normally do it...

ie. CH4 + O2 --> H2O + CO2 <--- Unbalanced. l=left, r=right

C's (l): 1 C's (r): 1
H's (l): 4 H's (r): 2
O's (l): 2 O's (r): 3

Those are the total number of elements on each side. Notice how we have the same number of C's, so we're good for that, for now. But we need 4 H's on each side...
So:

CH4 + O2 --> 2H2O + CO2 <--- I put a coefficient of 2 before H2O.
makes:

C's (l): 1 C's (r): 1
H's (l): 4 H's (r): 4
O's (l): 2 O's (r): 4

Now we have to balance the O's.

CH4 + 2O2 --> 2H2O + CO2 <--- I put a coefficient of 2 in front of O2

C's (l): 1 C's (r): 1
H's (l): 4 H's (r): 4
O's (l): 4 O's (r): 4

So it's balanced!
Listen. You shouldn't have to write out these tables everytime you add a new coefficient. You should be able to do it all in your head. But if oyu can't you can always put numbers right below the elements to kind of keep tab on everything. Anyways, you got the idea of how it works now, so all you have to do is practise practise...

http://dbhs.wvusd.k12.ca.us/Equations/Balance-Worksheet1.html
http://dbhs.wvusd.k12.ca.us/Equations/Balance-Worksheet2.html

There's 100 questions for you to practise with.
You know I just wasted a lot of my time writing this out. There are a lot of resources you could have looked up for answers to your question. If I knew you I'd expect some kind of sexual proposition, especially if you have an older (hot) sister. Learn to use the search engine THEN ask if you're clueless. lazy LAZY LAZY.