Year 10 Science · Unit 2 · Lesson 9

Writing and Balancing Chemical Equations

Challenge Worksheet

Name

Date

Class

Learning Goals

Identify and explain the flaw in changing subscripts rather than coefficients.
Provide a correctly balanced equation for iron oxide formation.
Articulate the law of conservation of mass in the context of balancing equations.

Go Deeper

Find the mistake

A student wrote this answer

"To balance the equation Fe + O₂ → Fe₂O₃, I noticed there were 2 iron atoms on the right but only 1 on the left, so I changed Fe to Fe₃ on the left. Then there were 3 oxygen atoms on the right, but O₂ only has 2, so I changed O₂ to O₃. My final balanced equation is: Fe₃ + O₃ → Fe₂O₃. Both sides now have 3 oxygen atoms and I think the iron atoms match too."

1. Identify the mistake(s) in the student's answer. Be specific about what the student changed and why that is not allowed.

Challenge 2 marks

2. Write the correctly balanced equation for iron reacting with oxygen to form iron(III) oxide (Fe₂O₃). Show your atom count for the balanced equation.

Challenge 2 marks

3. Explain why this kind of mistake is easy to make. What fundamental law of chemistry does changing subscripts violate, and why must we only use coefficients?

Challenge 2 marks

Show What You Know

1. Consider this equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (cellular respiration). Verify that this equation is balanced by counting all atoms on each side. Show your working.

Challenge 3 marks

2. A student claims: "Since both sides of an equation have the same atoms, no new atoms are created in a chemical reaction." Explain whether this is correct and which scientific law this demonstrates.

Challenge 2 marks

Wrap Up

In one sentence, what was the main idea of this lesson?