Question

How many grams of water could be made from 5.0 mol `H_2` and 3.0 mol `O_2`?

Answer 1

You need a stoichiometric equation to represent the formation of water:

Explanation:

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

Given the stoichiometry, dihydrogen is in deficiency, and ONLY `2.5*mol` dioxygen will react to give `5 *mol` water.

And this represents a mass of `5*cancel(mol)xx18.01*g*cancel(mol^-1)=90*g`.

What mas of dioxygen will remain after reaction?

Answer 2

90 g

Explanation:

The balanced equation is: `2H_2(g) + O_2(g) -> 2H_2O(l)`

From this you can see that 5 moles of hydrogen gas would react with 2.5 of the available 3 moles of oxygen gas, to form 5 moles of water.

The molar mass of water is 18 g/mol, so you would end up with 5 x 18 = 90 g of water.