Question

Octane is a hydrocarbon that is found in gasoline. Complete combustion of octane produces 8 L of carbon dioxide for every 9 L of water vapor (both measured at the same temperature and pressure). What is the ratio of carbon atoms to hydrogen atoms in a molecule of octane?

Answer 1

4C:9H

Step-by-step explanation:

Octane is a hydrocarbon that has the molecular formula C₈H₁₈, which means that the molecule has 8 carbon atoms and 18 hydrogen atoms.

Thus, the ratio of carbon atoms to hydrogen atoms is:

(8 carbon atoms) / (18 hydrogen atoms) = 4/9 C:H

Answer 2

`(4)/(9)`

Step-by-step explanation:

We start with the chemical equation for the combustion reaction of octane (
`C_(8) H_(18)`).

The combustion reaction is as follows:

`C_(8) H_(18)+(25)/(2)O_(2)`⇒
`8CO_(2)+9H_(2)O`

In this we need to consider some things:

• Temperature is constant
• Volume is equatable with the number of molecules (The number of molecules of Carbon, Hydrogen and Oxygen on both sides of the equation is the same)
• Pressure is constant

So, when a molecule of octane combusts, 8 molecules of Carbon Dioxide and 9 molecules of water are created. We can see then that the coefficients in the chemical reaction (the numbers accompanying the chemical formula) are proportional to moles and to volume.

Mathematically, the ratio of carbon atoms to hydrogen atoms would be
`(x)/(y)`, where x and y comes from
`C_(x) H_(y)`, or
`(8)/(18)`, which simplified is
`(4)/(9)`