Mass in a chemical reaction: using moles | Exit Quiz | Oak National Academy

What does stoichiometry mean in chemistry?

• The study of chemical reactions.

• Measuring elements and their ratios in reactions.

• The temperature changes in chemical reactions.

• The speed of chemical reactions.

Answer explanation

stoichiometry involves the measurement of elements and their ratios in chemical reactions, deriving from the Greek words 'stoicheion' (element) and 'metria' (to measure).

In a balanced chemical equation, what does the mole ratio of reactants and products tell us?

• The speed of the reaction.

• The physical states of the reactants and products.

• How many particles are involved in the reaction.

• The proportions of substances that react or are produced.

Answer explanation

The mole ratio indicates the proportions of substances that react or are produced in a chemical reaction, directly related to the balanced chemical equation.

The ___ is the sum of the relative atomic masses of all the atoms in a formula, representing the mass of a molecule relative to the mass of a carbon-12 atom.

Answer explanation

The relative formula mass (RFM/Mr) is the sum of the relative atomic masses of all the atoms in a formula, representing the mass of a molecule relative to the mass of a carbon-12 atom.

Which of the following statements best describes what the equation 2H₂ + O₂ → 2H₂O tells us?

• Two molecules of hydrogen react with one molecule of oxygen.

• Two moles of hydrogen are needed to react with one mole of oxygen.

• Four hydrogen atoms react with two oxygen atoms.

• 2 hydrogens reacts with oxygen to make 2 lots of water.

Answer explanation

Two moles of hydrogen react with one mole of oxygen to produce two moles of water, showing the reactants and products in the reaction.

Given the reaction: CH₄ + 2O₂ → CO₂ + 2H₂O, how many grams of CO₂ are produced when 16 g of methane (CH₄) reacts completely? Relative formula mass values: (CH₄ = 16) & (CO₂ = 44)

• 22 g

• 44 g

• 66 g

• 88 g

Answer explanation

16 g of CH₄ is 1 mole, which produces 1 mole of CO₂. Since the Mr of CO₂ is 44, 1 mole of CO₂ weighs 44 g.

Using the reaction: N₂ + 3H₂ → 2NH₃, calculate the mass of ammonia (NH₃) produced when 14 g of nitrogen react with hydrogen? (2 s.f.) Relative formula mass values: (N₂ = 28) & (NH₃ = 17)

Answer explanation

For 14 g of N₂, which is 0.5 moles, the reaction produces 1 mole of NH₃ (since the ratio of N₂ to NH₃ in the balanced equation is 1:2). Therefore, 1 × 17 = 17 g of NH₃ are produced.