Which equation obeys the law of conservation of mass?

2Fe + 3O2 → 2Fe2O3

4Fe + O2 → 2Fe2O3

Fe + O2 → Fe2O2

4Fe + 3O2 → 2Fe2O3

Question

Which equation obeys the law of conservation of mass?

2Fe + 3O2 → 2Fe2O3

4Fe + O2 → 2Fe2O3

Fe + O2 → Fe2O2

4Fe + 3O2 → 2Fe2O3

jfraser · Answer

We obey conservation of mass by $balancing$ chemical equations. Which reaction is balanced?

anonymous · Answer

The first one?

anonymous · Answer

NO! The fourth one?

anonymous · Answer

@JFraser

jfraser · Answer

pick one and stick with it

sweetburger · Answer

Look at the number of moles of Fe on the right side and make sure it is equivalent to the number of moles of Fe on the left side do the same process with oxygen so that there is and equivalent number of moles of Oxygen on both the left and ride side of the equation.

anonymous · Answer

You just need to make sure you have the same number of each element on both sides of the equation

anonymous · Answer

It was D and I got it correct. 
Thanks for all the help!