Question

How many moles of O2 are required to generate 18 moles of H2O in the given reaction? 2C8H18 + 25O2 16CO2 + 18H2O

Answer 1

Answer: 25 moles of oxygen gas will be required for the production of given amount of water.

Explanation:

This is a reaction of combustion of hydrocarbon. Combustion reaction states that when a hydrocarbon reacts with excess of oxygen it results in the formation of carbon dioxide and water.

For the reaction of combustion of hydrocarbon, the equation follows:

$2C_8H_{18}+25O_2\rightarrow 16CO_2+18H_2O$

By Stoichiometry of the reaction:

18 moles of water is produced by 25 moles of oxygen gas.

So, 18 moles of water will be produced from = $\frac{25}{18}\times 18=25mol$ of oxygen gas.

Hence, 25 moles of oxygen gas will be required for the production of given amount of water.

Answer 2

There's a slight error in your equation. I think you were trying to present it like this:

2C8H18 + 25O2 -> 16CO2 + 18H2O

Mole Ratio
O2 : H20
25 : 18
? moles : 18 moles
(18/18)×25 : 18 moles

25 moles : 18 moles

Final answer would be 25 moles of O2. :)

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