Question

Is `2H_2(g) + O_2(g) rarr 2H_2O(l)` the same as `H_2(g) + 1/2O_2(g) rarr H_2O(l)`?

Answer 1

Why not?

Explanation:

`2H_2(g)+O_2(g) rarr 2H_2O(l)`

`36*g` of reactants, and `36*g` of products..........

VERSUS.......

`H_2(g) + 1/2O_2(g)rarr H_2O(l)`

`18*g` of reactants, and `18*g` of products..........

Is mass conserved in each reaction? Well, clearly mass IS conserved. And while of course I cannot have half a molecule of dioxygen gas, I can certainly have a `16*g` quantity of `O_2(g)`, i.e. a HALF A MOLE quantity of dioxygen gas. The use of such fractional coefficients often makes the arithmetic involved in stoichiometry a bit easier, which of course is why they are used.