Question

robin and alex are discussing how water molecules form when hydrogen and oxygen atoms combine. they write the following chemical equation to explain the formation of water. h₂ + o₂ → h₂o however, alex has a different opinion and suggests that the chemical reaction can be better represented by the equation below. 2h₂ + o₂ → 2h₂o why does alex’s equation better represent the reaction? a. for every two molecules of water formed, one hydrogen atom is needed. b. the number of oxygen atoms is the same before and after the reaction. c. for every two molecules of water formed, two hydrogen atoms are needed. d. the amount of product formed should be more than the amount of reactants involved.

Explanation:

In a balanced chemical equation, the number of atoms of each element must be the same on both sides of the equation. In Alex's equation $2H_2 + O_2
ightarrow2H_2O$, the number of oxygen atoms (2) is the same before (in $O_2$) and after (in $2H_2O$) the reaction, and it is also balanced for hydrogen atoms.

Answer:

B. The number of oxygen atoms is the same before and after the reaction.