Given 2H2+ Oz--> 2H20 what mass of hydrogen is needed to create 125 g of water?

Question

i just need a more ‘in depth’ explanation that would be wonderful

Answer 1

Hello, Blt,

I'll assume the reaction is:

2H₂ + O₂ → 2H₂O [Oz is on my bucket list to visit]

We want 125 grams of water and need to know how much hydrogen is required.

This is the type of problem that makes the concept of moles so useful. The balanced equation tells us we need 2 moles of H₂ to produce 2 moles of H₂O (assuming 100% yield). Let's start by converting the 125 grams of water into moles of water:

The molar mass of water is 18.0 grams/mole. 125 g is: (125g)/(18.0 g/mole) = 6.94 moles of H₂O.

Since the molar ratio of water to hydrogen is 1:1, this means we need 6.94 moles of H₂.

Convert the 6.94 moles H₂ to mass by multiplying by the molar mass of H₂, which is 2 grams/mole:

(6.94 moles H₂)*( 2 grams/mole) = 13.89 grams (13.9 grams to 3 sig figs)

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Summary: The balanced equation will show the relationships between the reactants and products in terms of either 1) individual atoms, or 2) moles of the compounds. Since a mole is simply a shortcut for a large number, it is essentially the same as counting individual atoms. Instead of just one atom of H₂O, a mole tells us we have a few more (6.02x10^23) of the rascals. The ability to convert from moles to mass is an elegant feature and key to making chemical reactions economically feasible. 125 grams of water doesn't sound like much, but that represents 6.94 moles or (6.94)*(6.023x10^23) individual molecules of water. With today's technology, you might be able to count them out one-by-one, but try calculating the years it would take, even at 1 per second.

I hope this helps.

Bob