Posted by Momo on Tuesday, February 17, 2009 at 7:47pm.
Trial and error. Here is how you go about the first one. Rule 1. You must balance ONLY by changing the coefficients. You may NOT change any of the subscripts.
Al + Pb(NO3)2 ----> Al(NO3)3 + Pb
Look at the nitrate on the right side. There are 3 of them and 2 on the left so we know right away, if we are to use whole numbers, that we must multiply one by 2 and the other by 3.
Al + 3Pb(NO3)2 ==> 2Al(NO3)3 + Pb
Now you see we have 2 Al on the right. We can make Al balance by place a 2 as a coefficient on the left for Al. Now we have
2Al + 3Pb(NO3)2 ==> 2Al(NO3)2 + Pb
Now we see 3 Pb on the left and we can fix that by placing a 3 for Pb.
2Al + 3Pb(NO3)2 ==> 2Al(NO3)3 + 3Pb
We ALWAYS check it to see that everything balances.
I see 2 Al atoms on the left and right.
I see 3 Pb atoms on the left and on the right.
I see 6 NO3^- on the left and 6 on the right. So everything balances.
The others are done the same way. Post your work if you have problems. Check this yourself to make sure I didn't goof.