Given the reaction: C3H8 + 5 O2 → 3 CO2 + 4 H2O

Question

What is the total number of moles of O2 required to produce 1.5 moles of CO2?

A)

5.0

B)

2.5

C)

3.0

D)

1.5

Answer 1

you can use the balanced chemical equation to determine what the mole ratio is between substances ... on this one we have 5 mol O₂ to 3 mol CO₂, meaning that 1.5 mol of CO₂ produces

1.5 mol CO₂ x 5 mol O₂ / 3 mol CO₂ = 2.5 mol O₂

Answer 2

A balanced chemical equation is a ratio: this one shows that for every 5 moles O₂, 3 moles CO₂ are produced. Since there's a 5:3 ratio of O₂/CO₂,

((5 m O₂)/(3 m CO₂)) * 1.5 m CO₂ = 2.5 m O₂. Answer B.