Im really confused on how to balance these chemical equations we did in class today.. if someone could help me with these that would be great..
1. The solids aluminum and sulfur react to produce aluminum sulfide
2. Water and dinitrogen pentoxide gas react to produce aqueous hydrogen nitrate
3. The gases nitrogen dioxide and oxygen react to produce dinitrogen pentoxide gas
4. Ethane gas (C2H6) burns in air, producing carbon dioxide gas and water vapor
5. Aluminum oxide(s) decomposes when electricity is passed through it
6. Nickel (II) hydroxide(s) decomposes to produce nickel(II) oxide(s) and water
7. Heating sodium hydrogen carbonate(s) produces sodium carbonate(aq), carbon dioxide(g), and water

Im really confused on how to balance these chemical equations we did in class today..if someone could help me with these that would be great..
1. The solids aluminum and sulfur react to produce aluminum sulfide
2. Water and dinitrogen pentoxide gas react to produce aqueous hydrogen nitrate
3. The gases nitrogen dioxide and oxygen react to produce dinitrogen pentoxide gas
4. Ethane gas (C2H6) burns in air, producing carbon dioxide gas and water vapor
5. Aluminum oxide(s) decomposes when electricty is passed through it
6. Nickel (II) hydroxide(s) decomposes to produce nickel(II) oxide(s) and water
7. Heating sodium hydrogen carbonate(s) produces sodium carbonate(aq), carbon dioxide(g), and water
I'll do # 1 and #3, you do the others:
Al is a group 3 element, that means it has 3 electrons wanting to bond (valance electrons). The rule of 8 says atoms in compounds like 8 electrons around them, so Al could gain 5 or lose 3. Losing 3 is much more likely. (The lessor number of electrons is always the choice) Where are the 8? Those electrons from the previous shell as in Ne, the noble gas 3 elements before Al. If Al lost 3, it's ionic charge would be +3 because it has, now 3 more protons than electrons. Now for S, it is a group 6 element, so it has 6 valence electrons. To get 8 it could lose 6 (and be like Ne) or gain 2. Gain 2 is the choice so, then S has a ionic charge of -2. When Al and S form a compound, all the charges are balanced (otherwise it would be an ion), so that means aluminum sulfide is Al2S3 (+6 & -6 get it?). Simply put, the reaction is 2Al + 3S --> Al2S3. More complicated is the fact that sulfur actually exists as S8, so really the reaction is 16Al + 3S8 --> 8Al2S3 but that's advanced.

Now for #3: NO2 + O2 --> N2O5 (as defined from their names) is balanced by doing that atom balancing one at a time, like there 2 N's on the right so there has to be 2 N on the left (2NO2 + O2 --> N2O5 but the O's don't add up. They would if there was 1/2 of a O2, like 2NO2 + 1/2 O2 --> N2O5, but equation balancers don't like 1/2's of molecules so just multiply the entire equation by 2, now 4NO2 + O2 --> 2N2O5 is correct. Now you do the others.

Wow we are doing this in our webassing this year... all the Same problems! Wow

If you want some advice, make a new thread of your own please. There are often new people coming here, not knowing how the site works, etc and I just wanted to say that, just in case.