Answer:
4) 4Fe + 3O₂ → 2Fe₂O₃
Explanation:
4Fe + 3O₂ → 2Fe₂O₃
In this equation the numbers of atoms are same in both side. There are four iron and six oxygen atoms are present on left and right side of equation. That's why atoms are conserved. This equation completely followed the law of conservation of mass.
Law of conservation of mass:
According to the law of conservation mass, mass can neither be created nor destroyed in a chemical equation.
This law was given by french chemist Antoine Lavoisier in 1789. According to this law mass of reactant and mass of product must be equal, because masses are not created or destroyed in a chemical reaction.
The given question is incomplete. The complete question is:
In the chemical reaction: , with 8 grams of and 16 grams of and the reaction goes to completion, what is the excess reactant and how much of that would remain?
A) 6 grams of
B) 7 grams of
C) 8 grams of
D) 12 grams of
E) 14 grams of
Answer: A) 6 grams of 
Explanation:
To calculate the moles :
According to stoichiometry :
1 moles of 
require 2 moles of
Thus 0.5 moles of will require=
of
Thus is the limiting reagent as it limits the formation of product and is the excess reagent.
(4.0-1.0) = 3.0 moles of are left unreacted
Mass of remained=
Thus 6.0 g of will remain.
Answer:
Explanation:
In one mole of carbon, there are 6.02×10^23 atoms. So in two moles, there will be twice that: 1.204×10^24
