Starter quiz
- Given the relative atomic masses (Ar): C (12), O (16) Calculate the relative molecular mass (Mr) of carbon dioxide (CO₂).
- 44 ✓
- 28
- 192
- 0.75
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- What does the conservation of mass in a chemical reaction imply?
- Mass of products is always more than the mass of reactants.
- Mass of reactants is converted into energy.
- Mass of reactants equals mass of products. ✓
- Atoms are destroyed to conserve mass.
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- If 20 g of sodium reacts fully with 15 g of chlorine, how much sodium chloride is produced?
- '35 g' ✓
- For the equation __ N₂ + __ H₂ → __ NH₃, select the correct coefficients to balance it.
- 1, 3, 2 ✓
- 1, 2, 3
- 1, 3, 3
- 2, 3, 2
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- What does the equation 2H₂ + O₂ → 2H₂O tell us?
- Two molecules of hydrogen react with two molecules of oxygen.
- Two molecules of hydrogen react with one molecule of oxygen. ✓
- One molecule of hydrogen reacts with one molecule of oxygen.
- Two molecules of water are decomposed into hydrogen and oxygen.
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- Given the relative atomic mass values (Ar): H (1), S (32), O (16) Calculate the relative formula mass (Mr) of sulfuric acid.
- '98' ✓
Exit quiz
- 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.
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- 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. ✓
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- 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.
- 'relative formula mass' ✓
- 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.
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- 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
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- 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)
- '17 g' ✓
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.
- Chemical equations are most correctly interpreted in terms of molar ratios (i.e. 1 mole of A reacts with 2 moles of B).
- The molar ratios of the substances in a chemical reaction is known as stoichiometry, which means ‘measuring elements’.
- The stoichiometry of a reaction is shown by coefficients in a balanced equation. These molar relationships don't change.
- The moles of substance in a reaction can be determined using: mass(g) = Mr × moles (& the stoichiometry of reaction).
Common misconception
Pupils struggle to recall the order of steps required to mathematically process the available information in order to answer the question.
Colour-coding the steps can help pupils remember how many steps are involved. Much practice and perseverance is needed to create and maintain the memory pathway of the mathematical processing.
Keywords
Stoichiometry - Stoichiometry refers to the molar ratio of the reactants and products in a chemical reaction.
Relative formula mass - The relative formula mass (RFM or Mᵣ) of a substance is the sum of the relative atomic masses of all the atoms in its formula.
Mole - 1 mole of a substance is 6.02 × 10²³ particles of it. The mass of a mole of a substance is its relative mass in grams.
Coefficient - A coefficient is the number placed in front of a chemical formula to balance an equation; it multiplies all the atoms in the formula and shows the ratio of substances in a reaction.
Balanced symbol equation - A balanced symbol equation represents a chemical reaction using symbols and coefficients to ensure that the number of atoms of each element is equal on both sides of the equation.