Question

Using the equation 2 H2 + O2 ---> 2 H2O determine how many grams of oxygen will be needed to form 100.0 grams of water?

Answer 1

Approx. `89*g`....

Explanation:

We got the stoichiometric equation...

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

`"Moles of water"=(100*g)/(18.01*g*mol^-1)=5.55*mol`

And, therefore, we need an equivalent quantity of dioxygen gas... a mass of `5.55*molxx1/2xx32.00*g*mol^-1=??*g`..

Answer 2

177.62g (2.d.p)

Explanation:

Equation: `2H_2+O_2 -> H_2O`

First, we need to calculate the moles of water.

`"moles" = "mass"/"molar mass"`
mass: 100g
molar mass: `1.008times2+16 = 18.016`

`"moles"=100/18.016 = 5.55062167`

Now, we have to look at the ratio:

hydrogen:oxygen:water = `2:1:1`

Therefore, looking at water and oxygen, they have the same ratio of 1:1. That means that the moles of water is equal to the moles of oxygen.

Using the same equation as earlier, we already know the following:
moles = 5.55062167
molar mass = `16times2 = 32`

Rearranging the equation gives me:

`"mass" = "moles"times"molar mass"`

`"mass" = 5.55062167 times 32 = 177.62g`