H 1

[Snigdha Uppu 1G]

It appears that balancing the chemical equation Cu 1 SO 2 S
CuO 1 S would be simple if we could just add another O atom to the
product side: Cu 1 SO 2 S CuO 1 S 1 O. (a) Why is that balancing
procedure not allowed? (b) Balance the equation correctly.

I am confused about part a.

[Chem_Mod]

In the future, please try typing your chemical equation like this: Cu + SO2 --> CuO + S, separating the reactants and products as well as keeping compound subscripts attached to the element symbols. Otherwise it makes it extremely hard to read. You can't just add an O to the products side because then you would be changing the entire reaction. To balance, manipulate the coefficients in front of each compound so the number of each element is the same on both sides.

[EmilyJoo_1G]

(a) That procedure is not allowed because adding an oxygen atom violates the law of conservation of mass. It's impossible for another oxygen atom to just show up at the end of a reaction if it wasn't present in the reactants to begin with.

(b) 2Cu + SO2 ~~> 2CuO + S

Hope that helps!

[Sanjana K - 2F]

Also, oxygen won't generally be present in a reaction as one oxygen atom alone. Oxygen is a diatomic molecule, so it'll only show up in a reaction as O2. Here's a list of other diatomic molecules (hydrogen, oxygen, fluorine, bromine, iodine, nitrogen, chlorine.. AKA HOFBrINCl).

[Aprice_1J]

Something that one of the LA's taught me that is helpful if you're stumped on a balancing equations problem is to writing it as a system of equations. For Cu + SO2 --> CuO + S you would put a letter in front of each of the different parts and then write out an equation for every element. Cu would be 1a=1c. S would be 1b=1d and then O would be 2b=1c. From here you would solve for the unknown. For O I would try making c equal to 2 and b equal to 1. That would then mean that a would equal 2 and d would equal 1 which checks out. It's just a nice way to go about it if you are stuck just looking at it and trying to figure it out.

[Ashley Fang 2G]

Another tip is to generally start out balancing the element that shows up the least often in the equation and then work from there, eventually getting to elements in diatomic molecules such as H2 or O2 that stand alone and are easy to balance by themselves (just add a coefficient in front)

[Ethan Low 1L]

A good practice might be to write out a table on the side for both the reactants and the products, I saw my TA do this in discussion. Also try and balance out the elements that appear the least FIRST, then work your way through the other elements!

Hope that helps (: