Physical Science
posted by Amber on .
Balancing Equations
Al+N2>AlN
NH4NO3>N2O+H2O
Pb(NO3)2+HCl>PbCl2+HNO3

Are you balancing these by inspection or by redox methods? I assume by inspection this early in the course. I will do the first one and you do the others.
Al + N2 ==> AlN
Rule 1. You may NOT change any of the subscripts. You MAY change coefficients ONLY.
By inspection, we can see Al is balanced and N is not. We can balance N by placing a 2 for AlN. Like so.
Al + N2 ==> 2AlN
Of course that messes up the Al but we can fix that by placing a 2 on the left for Al. Like so.
2Al + N2 ==> 2AlN
Now, we ALWAYS check it to make sure it is balanced. I see 2 Al on the left and 2 Al on the right. OK.
I see 2 N on the left and 2 on the right. OK.
So, it's balanced.
Now you do the others. I shall be happy to check your work. Start the the last one. That's a little easier than #2. 
Pb(NO3)2+HCl>PbCl2+HNO3
Pb(NO3)2+2HCl>PbCl2+HNO3
I'm not sure. Long ones are a bit more difficult. 
You can ALWAYS tell if your answer i correct by checking it.
I see 1 Pb on the left and 1 on the right. OK>
I see 2 N on the left and 1 on the right. NO GO. We can stop there becasue we know it isn't balanced. Howver, H doesnt balance either for there are 2 on the left and 1 on the right. Oxygen has 6 on the left and 3 on the right. With Pb and Cl OK, that just leaves you to fix the HNO3 so it balances H, N and O all at the same time. 
Pb(NO3)2+2HCl>PbCl2+2HNO3

So would HNO3 become 3HNO?

Rule #1. You may NOT change any subscripts. You MAY change ONLY coefficients.

I have no idea then.. I'm lost.

You can't be lost. You are so CLOSE it would bite if it could.
Let's go over it bit by bit.
There is 1 Pb on the left and 1 on the right so that is OK.
There are 2 Cl on the left and 2 on the right. That is OK. You had to place a 2 in front of the HCl so the Cl would balance. That's great. So what's left.
You look on the right and the H atoms don't balance. You now have 2 on the left so put a 2 in front of the HNO3. That will take care of the H atoms for we now have 2 on the left (from 2HCl) and 2 on the right (from 2HNO3). That leaves N and O so we check them out.
You have 2 N on the left (from Pb(NO3)2) and 2 on the right (from 2HNO3). N is OK. What about O. We have 6 O on the left (from Pb(NO3)2) and we have 6 O on the right (from 2HNO3). Done. All you needed to do was balance the H and everything else fit into place. 
Oh thank you! You were a bunch of help.

Do you want to do the middle one. It's easy. Balance N first. Balance H next. Balance O last.

Yeah, easy for you to say! ;(
NH4NO3>N2O+H2O
2N 2(H4)2?NO3>2NO+H2O
I tend to overthink a lot...I make it harder than it seems. 
You have that right.
You can't change anything but the coefficients. On the last problem you tried to make HNO3 into 3HNO and that isn't legal. On this one, you have changed the NH4NO3 into something else. What I don't know. That isn't legal either. Leave everthing as is.
NH4NO3 ==> NO + H2O.
Now, ask yourself, "How many N atoms do I see on the left?" and what do you say? 
I see 1 N on the left.
And then on the right side,
I see N2
so I put a '2' by the N on the left. 
I see 2 Ns on the left. I see NH4NO3. True the Ns are in two different places but that doesn't matter. There are two N atoms on the left. How many do you see on the right, from N2O?

I see 1 N on the right. So it is unbalanced.

The equation you started with says
NH4NO3 ==> N2O + H2O.
There are 2 N atoms on the left. There are TWO N atoms on the right (from N2O). Is that where we are messing up. These computers won't write subscripts so we must imagine them. The 2 in N2O is a subscript. If that is the problem I can fix that in a hurry. 
NH_{4}NO_{3} ==> N_{2}O + H_{2}O

Oh.

So N balances. There are 2 N atoms on the left from NH4NO3 and 2 on the right from N2O. Thus, we leave the coefficient of 1 there for NH4NO3 and the coefficient of 1 for N2O.
next, balance H.
I see 4 H stoms on the left. How many on the right and what do we do? 
There are 2 H atoms on the right.
Now we have to balance them.
Do we add a 4 by the H? 
yes and no.
We have 4 H atoms on the left from NH4NO3. We have 2 H atoms on the right (you are correct) from H2O. What can we make the coefficient for H2O to make that 4 H on the right? There is a 1 there now. We want to put a coefficient in front of the H2O so that ? x 2 = 4. What would that coefficient be? 
It would be 2 because 2x2 is 4..which equals the total number of the coefficient on the left.
So the coefficients on the right have to equal the total numbers of coefficients on the left? 
No. It isn't necessary to make coefficients equal. It is necessary to make the atoms equal.
You have 4 H atoms on the left and you must have 4 on the right. The coefficient of 1 is in place now in front of the H2O as in 1H2O. The coefficient multiplies everything after it in the molecule so 1 x 2 means we have 2 H atoms. 1 x 1 = 1 and we have 1 O atom. So we want to make 4 atoms on the right. What number must the coefficient be so that the coefficient x 2 (from the H2O) will equal to 4? 
I should have saic we want to make the H atoms on the right 4 so what can we multily the molecule by (what is the coefficient) so that the coefficient x 2 (the 2 is from H2O) = 4 H atoms on the right?

2?

Of course. So what do we have?
We have a 1 in front of the NH4NO3 and a 1 in front of the N2O and a 2 in front of the H2O. We know N balances (2 N atoms on each side) and H balances (4 H atoms on each sisde) and that leaves just O atoms. They are supposed to balance if everything else balances. See if they do? Count O atoms on the left and O atoms on the right. How many do you see? 
That's right. There are 3 O atoms on the left (from NH4NO3; i.e., 3 subscript x 1 coefficient = 3) and 3 on the right (1 from N2O; i.e., 1 subscript x 1 coefficient = 1 and 2 from 2H2O; i.e., 1 subscript x 2 coefficient = 2 and 1 from N2O + 2 from 2H2O = 3 O atoms on the right.) So now you have all three done. Talk to your instructor during office hours and tell him/her what kind of trouble you are having. I wish I had you and a blackboard and about 15 minutes. We could get this done. But we can't trade personal information on these web sites. Anything else? I hope you come back if you need more help on anything.

Thank you so very much

when the equation NH4NO3M2O os ba;anced, what is the total of all the coefficients?

how are reactants and products treated the same in a chmical reaction how are they treated diffrently

The 1st one is 2Al+N2 > 2AlN
The 2nd one is NH4NO3 > N2O+2H20
The 3rd one is 
The 1st one is 2Al+N2 > 2AlN
The 2nd one is NH4NO3 > N2O+2H20
I'll let bob handle 3.