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Science lesson plan · 12th grade (Year 13 in England) · 30 minutes

Find the limiting reactant and how much product forms

Chemical reactions, acids and bases

CCSS NGSS.HS-PS1-7England: GCSE Chemistry: Quantitative chemistry (limiting reactants, Higher)

Objective and success criteria

Students will: Find the limiting reactant and how much product forms.

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: Moles and reacting masses; Percentage yield

Leads to: the next skill in this area.

Materials: Teacher demo or video, Indicator color chart, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 4 min

  • Quick retrieval from earlier learning (Moles and reacting masses; Percentage yield). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. How many moles are in 9 g of water (H₂O, Mr = 18)? → 0.5 molPrompt: moles = mass ÷ Mr
  2. A reaction could make 25 g of product in theory, but 20 g was actually collected. What is the percentage yield? → 80 %Prompt: percentage yield = actual mass ÷ theoretical mass × 100
  3. What is the mass of 4 mol of magnesium oxide (MgO, Mr = 40), in g? → 160 gPrompt: mass = moles × Mr

Hook · 3 min

  • Drop an antacid tablet in water (or show a clip) and ask whether a new substance is being made.
  • Share the objective: Find the limiting reactant and how much product forms. Read the success criteria together.

I do: model it · 7 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Example: CHâ‚„ + 2Oâ‚‚ → COâ‚‚ + 2Hâ‚‚O. 1 mol of methane is mixed with 1 mol of oxygen. Which is the limiting reactant?
  • Step 1: methane: 1 ÷ 1 = 1; oxygen: 1 ÷ 2 = 0.5
  • Step 2: So the answer is: oxygen
  • Answer: oxygen
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 6 min

  • Do these together. Students try each step on whiteboards before you reveal it.
  • Use the hints as prompts rather than giving the answer.
  1. CH₄ + 2O₂ → CO₂ + 2H₂O. 3 mol of methane is mixed with 7 mol of oxygen. Which is the limiting reactant? (methane / oxygen) → methanePrompt: Divide each amount by its number in the equation.
  2. CH₄ + 2O₂ → CO₂ + 2H₂O. 5 mol of methane reacts with 8 mol of oxygen. What is the maximum amount of carbon dioxide that can form, in mol? Give 2 decimal places if needed. → 4 molPrompt: Find the limiting reactant first.

You do: independent practice · 7 min

  • Students work on the student sheet. Circulate and check the first two answers of every student early.
  • Students who finish: write a question of their own for a partner, with the answer.

The 6 questions are on the student sheet below, with answers in the key.

Exit ticket · 3 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. CH₄ + 2O₂ → CO₂ + 2H₂O. 5 mol of methane is mixed with 5 mol of oxygen. Which is the limiting reactant? (methane / oxygen) → oxygenPrompt: Divide each amount by its number in the equation.
  2. N₂ + 3H₂ → 2NH₃. 6 mol of nitrogen reacts with 1 mol of hydrogen. What is the maximum amount of ammonia that can form, in mol? Give 2 decimal places if needed. → 0.67 molPrompt: Find the limiting reactant first.

Watch out for

  • Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
  • Remembering facts without the reason: ask "why?" and "what is the evidence?"

Support and stretch

Support

  • Review first: Moles and reacting masses.
  • Use concrete materials: teacher demo or video.
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-12.

Free lesson plan from eurekami.com/lesson-plan-builder

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Find the limiting reactant and how much product forms

Name

Date

Score/ 6

  1. Question 1

    Mg + 2HCl → MgCl₂ + H₂. 6 mol of magnesium reacts with 2 mol of hydrochloric acid. What is the maximum amount of hydrogen that can form, in mol? Give 2 decimal places if needed.

    Answermol

  2. Question 2

    N₂ + 3H₂ → 2NH₃. 4 mol of nitrogen is mixed with 5 mol of hydrogen. Which is the limiting reactant?

    • A. nitrogen
    • B. hydrogen

  3. Question 3

    Doubling the amount of the reactant in excess will…

    • A. not change the amount of product
    • B. double the product
    • C. halve the product
    • D. stop the reaction

  4. Question 4

    N₂ + 3H₂ → 2NH₃. 2 mol of nitrogen reacts with 8 mol of hydrogen. What is the maximum amount of ammonia that can form, in mol? Give 2 decimal places if needed.

    Answermol

  5. Question 5

    N₂ + 3H₂ → 2NH₃. 2 mol of nitrogen is mixed with 8 mol of hydrogen. Which is the limiting reactant?

    • A. nitrogen
    • B. hydrogen

  6. Question 6

    Why is one reactant often used in excess in industry?

    • A. To slow the reaction down
    • B. To make sure all of the more expensive reactant reacts
    • C. Because excess reactants are free
    • D. To make the product impure on purpose

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Answer key: Find the limiting reactant and how much product forms

  1. 1. 1 mol

  2. 2. B. hydrogen

  3. 3. A. not change the amount of product

  4. 4. 4 mol

  5. 5. A. nitrogen

  6. 6. B. To make sure all of the more expensive reactant reacts