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Balancing Chemical Equations

Saint Nick

Saint Nick

Lifer
I'm having a hard time. This isn't for a class, but rather for a chemistry placement exam that I have coming up this Saturday and I'm just brushing up on it all. Here's one:

__C6H6 + __O2 --> __H2O + __ CO2

This particular example was pulled from an about.com worksheet for all of those who think I'm trying to get you guys to do my homework.

So, do you guys have any tips on how to start on these things? Thats my problem, is where do I start?

Here's the worksheet:
http://chemistry.about.com/library/formulabalance.pdf
And the answers:
http://chemistry.about.com/lib...rmulabalanceanswer.pdf
 
Put 1 in all the blanks. And when they complain, yell "I don't pay attention to posted speed limits, why the hell would I care about the law of conservation of matter?!" Then leave.
 
When i start, i just balance the first atom listed, and then the second, and so on, and make adjustments as necessary.

EDIT: you guys sure take things seriously around here.... Lol...
 
Number of carbon atoms equals molecules of CO2. Number of hydrogens/2 equals water molecules. Count up number of Oxygens from the total of water and CO2, and put that many O2 in. If you have a non-integer value for O2, multiply everything by 2.

Example from above:
C6H6 gives 6 CO2 and 3H2O. That gives a total of 15 O's, which is 7.5 O2. Multiply everything by 2.
Answer:

2 C6H6 + 15 O2 gives 12 CO2 + 6 H2O

That'll be $10, I'll send you my paypal. 😛
 
Originally posted by: videogames101
When i start, i just balance the first atom listed, and then the second, and so on, and make adjustments as necessary.
Click to expand...

:thumbsup:
That's how I learned it as well. It just takes Trial-and-Error sometimes, and others you are able to see it right away
 
Originally posted by: videogames101
When i start, i just balance the first atom listed, and then the second, and so on, and make adjustments as necessary.

(thats my sorry excuse for an explanation, but honestly, it all seems easy as someone who has an IQ of around 150..)
Click to expand...

Inflating your ego on ATOT eh!? Next time someone in a 400+ level course posts an outrageous math/sci/engineering problem, I expect you to be there solving it! With ease!
 
you could always break it down into a set of algebraic equations, but really, it's a matter of satisfying constraints. start with the most constrained thing (C) and work your way through.
 
You'll get a hang of it after a while...easiest way is to find out which element is most easily isolated - in this case, it's carbon on the right side. You know you need 6 to match the left side...but then you start matching up the hydrogens and oxygens and you realize that you have 15/2 so you multiply everything else by two to get a whole number.

It's just simple algebra dressed up...it'll get harder, so learn quickly 😉
 
Originally posted by: jndietz
I'm having a hard time. This isn't for a class, but rather for a chemistry placement exam that I have coming up this Saturday and I'm just brushing up on it all. Here's one:

__C6H6 + __O2 --> __H2O + __ CO2

This particular example was pulled from an about.com worksheet for all of those who think I'm trying to get you guys to do my homework.

So, do you guys have any tips on how to start on these things? Thats my problem, is where do I start?

Here's the worksheet:
http://chemistry.about.com/library/formulabalance.pdf
And the answers:
http://chemistry.about.com/lib...rmulabalanceanswer.pdf
Click to expand...

just look at the ratios

1 C6H6 on the left =6 CO2 on the right and 3 H2O on the right to get them to match them up


that means for every 1 C6H6 you need 6 CO2

1 C6 H6 -> 6 CO2 + 3 H2O to get the C's and H to match up

if you have something that is just one element H2 , O2 etc by itself fill those out LAST

usually you want to look at the most complex compound and start with 1 of those

and just figure out the ratios you need


X C6H6 + ?? O2 -> 6X CO2 + 3X H2O

now C's and H's are balanced so you just have to balance O's

there is 15X O's on the right so that is 7.5 O2's

X C6H6 + 7.5X O2 + 6X CO2 + 3X H2O


1 C6H6 + 7.5 O2-> 6 CO2 + 3H2O

if you cannot use decimals just double it

2 C6H6 + 15 O2 -> 12 CO2 + 6 H2O

-------------------------------------------------

the best tip I have is start with the most complex thing first and try to balance around that






 
A few of you guys have come up with 2, 15, 12, and 6 for coefficients. I am doing a method that I found on a teacher's website and I got the answer that is on the about.com answer key of 2, 7, 6, and 4.

What the heck?
 
They fail at chemistry? Can you post their reasoning? I'm in my third year of my PhD...if I can't do the HS shit, I'm in trouble.
 
Originally posted by: jndietz
A few of you guys have come up with 2, 15, 12, and 6 for coefficients. I am doing a method that I found on a teacher's website and I got the answer that is on the about.com answer key of 2, 7, 6, and 4.

What the heck?
Click to expand...

It's pretty easy dude. Conservation of matter. You gotta have the same number of elements on both sides. Having 2x C6H6 on the left would give you 12 C. The product should also be 12 C. If the coefficient was 4, you would only have 4 C, which defies conservation of matter. The answer posted by mchammer is correct.
 
I typed the example wrong.. thats why. LOL! You guys did it right!

Thanks for the help on that "toughy"...

Now, my next question is, what about ions? I have a very simple example here regarding table salt:

__Na+ + __Cl- --> __NaCl

I know that the coefficients are supposed to be 2, 2, and 1. But why? How do these ions come into play?
 
Originally posted by: TecHNooB
Originally posted by: videogames101
When i start, i just balance the first atom listed, and then the second, and so on, and make adjustments as necessary.

(thats my sorry excuse for an explanation, but honestly, it all seems easy as someone who has an IQ of around 150..)
Click to expand...

Inflating your ego on ATOT eh!? Next time someone in a 400+ level course posts an outrageous math/sci/engineering problem, I expect you to be there solving it! With ease!
Click to expand...

Well somewhat ego, but also, I'm explaining that this method might not do much good, because it's not really that efficient.... so quick to judge me, hmm! also, IQ != workable knowledge
 
Originally posted by: jndietz
I typed the example wrong.. thats why. LOL! You guys did it right!

Thanks for the help on that "toughy"...

Now, my next question is, what about ions? I have a very simple example here regarding table salt:

__Na+ + __Cl- --> __NaCl

I know that the coefficients are supposed to be 2, 2, and 1. But why? How do these ions come into play?
Click to expand...

Nope, the answer is 1, 1, and 1. Each atom is half the molecule. 2 halves make a whole. Look at the stoichiometry. The two combine in a 1:1 ratio.

Now, Alumina, for example, has Al3+ and O2-, so the ratio is Al2O3, giving +6 and -6 to cancel out.
 
Originally posted by: videogames101
When i start, i just balance the first atom listed, and then the second, and so on, and make adjustments as necessary.

(thats my sorry excuse for an explanation, but honestly, it all seems easy as someone who has an IQ of around 150..)
Click to expand...

OP, make a note. People with and IQ < 140 require the services of a TI-89 and an ouija board to efficiently balance chemical equations.
 
Originally posted by: George P Burdell
Originally posted by: videogames101
When i start, i just balance the first atom listed, and then the second, and so on, and make adjustments as necessary.

(thats my sorry excuse for an explanation, but honestly, it all seems easy as someone who has an IQ of around 150..)
Click to expand...

OP, make a note. People with and IQ < 140 require the services of a TI-89 and an ouija board to efficiently balance chemical equations.
Click to expand...

wtf, i was just pointing out the inefficiency of the method...
 
Originally posted by: TecHNooB
Originally posted by: videogames101
When i start, i just balance the first atom listed, and then the second, and so on, and make adjustments as necessary.

(thats my sorry excuse for an explanation, but honestly, it all seems easy as someone who has an IQ of around 150..)
Click to expand...

Inflating your ego on ATOT eh!? Next time someone in a 400+ level course posts an outrageous math/sci/engineering problem, I expect you to be there solving it! With ease!
Click to expand...

Um, your question is no where around 400+ level. I took Chem sophomore year of high school and we did balancing equations.
 
Originally posted by: legoman666
Originally posted by: TecHNooB
Originally posted by: videogames101
When i start, i just balance the first atom listed, and then the second, and so on, and make adjustments as necessary.

(thats my sorry excuse for an explanation, but honestly, it all seems easy as someone who has an IQ of around 150..)
Click to expand...

Inflating your ego on ATOT eh!? Next time someone in a 400+ level course posts an outrageous math/sci/engineering problem, I expect you to be there solving it! With ease!
Click to expand...

Um, your question is no where around 400+ level. I took Chem sophomore year of high school and we did balancing equations.
Click to expand...

we're doing balancing equations and I'm a freshmen in High School, rofl...
 
easy

C6 --> 6 CO2 = you need 6 O2

H6 --> 3 H2O = you need 3 O (1.5O2).

since you can't have 0.5 O2 (well you can, sorta, but for the purpose of balancing you can't), you just double everything.

final equation = 2 C6H6 + 15 O2 --> 12 CO2 + 6 H2O
 
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