If 3.8 g of F2(g) is consumed in the reaction, how many moles of O2(g) will be needed?

Question

Equimolar amounts of F2(g) and O2(g) are placed in a previously evacuated rigid container, where they react according to the equation below.

2F2(g)+O2(g)⇄2OF2(g)                    ΔHorxn=+49.4kJ/molrxn

If 3.8 g of F2(g) is consumed in the reaction, how many moles of O2(g) will be needed?

Answer 1

First you must convert grams of F₂ into moles using the molar mass. Each atom of F = 18.998 since there are two you multiple that number by 2 to get molar mass of F₂ = 37.996

Then you set up dimensional analysis to convert grams to moles.

3.8 g F₂ x 1 mole ₌ 0.100 moles F₂

37.996 g

Looking at the chemical equation to see the coefficient (number before compounds) to determine the ratio. Looks like in this equation it takes 2 F₂ for every 1 O₂

That means it will only require half of the moles that F₂ required.

0.100 moles/2 = 0.0500 moles of O₂ is your answer