Question

How many molecules of oxygen react with 20 molecules of propane?

Answer 1

`"70"` molecules of oxygen will react with `20` molecules of propane.

Explanation:

Balanced Equation

`"2C"_2"H"_6 + "7O"_2"` `rarr` `"4CO"_2 + "6H"_2"O"`

The ratio of propane to oxygen is `(2"molecules C"_2"H"_6)/(7"molecules O"_2")`

Calculate the number of molecules of oxygen that will react with 20 molecules with propane.

Multiply the given number of molecules of propane by the ratio of propane and oxygen with oxygen in the numerator.

`20color(red)cancel(color(black)("molecules C"_2"H"_6))xx(7"molecules O"_2)/(2color(red)cancel(color(black)("molecules C"_2"H"_6)))="70 molecules O"_2"`