RPAL Mole Ratios

Question 1

What is a mole ratio in a chemical reaction?

Accepted Answer

The ratio of moles of one substance to moles of another, derived from the balanced equation

Answer

Mole ratios come directly from the stoichiometric coefficients in the balanced equation and relate moles of any two substances in the reaction.

Question 2

In the balanced equation 2H₂ + O₂ → 2H₂O, what is the mole ratio of H₂ to H₂O?

Accepted Answer

2:2 (or 1:1)

Answer

The coefficients 2 (H₂) and 2 (H₂O) give a mole ratio of 2:2, which simplifies to 1:1.

Question 3

For N₂ + 3H₂ → 2NH₃, what is the mole ratio of H₂ to NH₃?

Accepted Answer

3:2

Answer

The coefficients are 3 for H₂ and 2 for NH₃, giving a 3:2 mole ratio.

Question 4

Why must an equation be balanced before using mole ratios?

Accepted Answer

Because mole ratios are derived from stoichiometric coefficients, which are only correct in a balanced equation

Answer

Stoichiometric coefficients in a balanced equation reflect the law of conservation of mass; incorrect coefficients give wrong mole ratios.

Question 5

Using the mole ratio, if you have 4 mol H₂ reacting via 2H₂ + O₂ → 2H₂O, how many moles of O₂ are needed?

Accepted Answer

2 mol O₂

Answer

The H₂:O₂ mole ratio is 2:1, so 4 mol H₂ requires 4 × (1/2) = 2 mol O₂.

RPAL - Reactants, Products, and Leftovers Practice Test