Question

In the equation `2C_2H_2(5) + 5O_2(5) -> 4CO_2(g) + 2H_2O(g)`, how many grams of oxygen gas are needed for the complete combustion of `1.8 * 10^2` `g` of acetylene?

Answer 1

About `553.6` grams of oxygen are used in this combustion.

Explanation:

Molecular mass of acetylene: `2 * MM_C + 2 * MM_H`
`MM_C` = Molecular mass of carbon
`MM_H` = Molecular mass of hydrogen

So, `2 * 12 + 2 * 1 = 26` grams/mole

`"Mass used in combustion"/"molecular mass" = "moles used in combustion"`

`(180cancel(" grams"))/(26 cancel(" grams")/"mole")= 6.92 " moles"`

According to the main equation, to 2 moles of acetylene, 5 moles of oxygen are used. `MM_O = 2 * 16 = 32` grams/mole

So, if we use `6.92` moles of Acetylene, `x` moles of oxygen will be necessary.

`x = (6.92 * 5)/2 = 3.46 * 5 = 17.3` moles of oxygen.
`17.3 cancel("moles") * 32 "grams"/cancel("mole") = 553.6` grams of oxygen.