Starter quiz
- Match the following terms to the correct definition.
- relative atomic mass⇔the average mass of the atoms of an element compared to carbon-12 ✓
- relative formula mass⇔the sum of the relative atomic masses of all the atoms in a formula ✓
- Avogadro's constant⇔the number of particles in one mole of a substance ✓
- The formula for ammonium nitrate is NH₄NO₃. Which of the following ratios are correct?
- The ratio of nitrogen to oxygen is 2 : 3. ✓
- The ratio of nitrogen to hydrogen is 1 : 2. ✓
- The ratio of oxygen to hydrogen is 3 : 4. ✓
- The ratio of oxygen to nitrogen is 2 : 3.
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- Chemical equations represent how the atoms in the ______ rearrange to form the products.
- 'reactants' ✓
- Which of the following is the equation which links mass, relative formula mass and amount of substance?
- mass = amount of substance × relative formula mass ✓
- mass = amount of substance ÷ relative formula mass
- amount of substance = relative formula mass × mass
- amount of substance = relative formula mass ÷ mass
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- True of false? The following equation is balanced: C₂H₄ + 2O₂ → 2CO₂ + 2H₂O.
- True
- False ✓
- Calculate the relative formula mass for calcium carbonate, CaCO₃. Relative atomic masses: Ca = 40; C = 12; O = 16.
- '100' ✓
Exit quiz
- Match the following key terms to the correct definitions.
- limiting reactant⇔the reactant that completely reacts during a reaction ✓
- excess reactant⇔a reactant that is left over at the end of the reaction ✓
- theoretical yield⇔the maximum calculated mass of product expected from a reaction ✓
- mole⇔the unit for amount of substance ✓
- Which of these statements about the equation are true? 2H₂ + O₂ → 2H₂O.
- One mole of hydrogen reacts with one mole of oxygen.
- One mole of oxygen reacts with two moles of hydrogen. ✓
- Two moles of water are formed for every two moles of hydrogen reacted. ✓
- Two moles of oxygen are needed to form two moles of water.
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- True or false? In a chemical reaction there are the same number of atoms in the products as there were in the reactants.
- True ✓
- False
- A student oxidises magnesium in a Bunsen burner flame. The oxygen is in excess. 2Mg + O₂ → 2MgO. How many moles of magnesium oxide would form from eight moles of magnesium?
- '8' ✓
- Which is the limiting reactant if 6 moles of methane reacts with 4 moles of oxygen? CH₄ + 2O₂ → CO₂ + 2H₂O.
- methane
- oxygen ✓
- carbon dioxide
- water
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- A student oxidises 2.0 g of magnesium in a Bunsen burner flame. The oxygen is in excess. 2Mg + O₂ → 2MgO. What mass of magnesium oxide would form from 2.0 g of magnesium? Give your answer to 2 s.f.
- '3.3' ✓
Worksheet
Presentation
Video
Lesson Details
Key learning points
- In a chemical reaction, the atoms in reactants are rearranged and are the same atoms that are in the products.
- A theoretical yield is calculated using the stoichiometry of a balanced equation & relevant mathematical relationships.
- The number of moles of limiting reactant available is used to calculate the theoretical yield of a reaction.
- If a reactant is added in excess, not all of it will react and some will be found in the final product mixture.
- A limiting reactant is one that restricts the amount of product that can form from the available particles.
Common misconception
Pupils sometimes fail to understand that excess reactant particles remain in the reaction mixture after the reaction.
Provide a balanced equation and challenge pupils to draw diagrams of a final mixture, stressing that excess particles would also be present. Challenge pupils to consider how the product could be extracted from the excess particles.
Keywords
Limiting reactant - The reactant that completely reacts, thereby determining the maximum amount of product that can be formed in a chemical reaction. All other reactants will be present in excess.
Excess reactant - Any reactant present in a greater amount than is necessary to completely react with the limiting reactant.
Theoretical yield - The maximum calculated mass of product expected to form from a given amount of reactants.
Mole - A mole of a substance contains 6.02 × 10²³ particles of it. The mass of one mole of a substance is its relative mass in grams.
Stoichiometry - The molar ratio of the reactants to the products in a chemical reaction.