Balancing equations and the reactivity series
Atoms are never created or destroyed in a reaction — only rearranged. Balancing is simply making the page agree with that fact.
Lesson overview
What you'll learn in this lesson
Understand chemical reactions as the rearrangement of atoms, represented by word and symbol equations
Key learning points
- • Conservation of mass
- • A reliable balancing method
- • The reactivity series
- • Displacement and extraction
This lesson at a glance
- 30 minutes
- 24 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 24
Visual introductionPicture this
Balancing equations and the reactivity series
Atoms are never created or destroyed in a reaction — only rearranged. Balancing is simply making the page agree with that fact.
In a nutshell
Understand chemical reactions as the rearrangement of atoms, represented by word and symbol equations
What you already know
Part 2 of 24
Before we start
What you already know
You should already know how to read chemical formulae and that mass is conserved in reactions.
Key words
Part 3 of 24
Key words
Words you'll need today
- Reactant
- A substance you start with.
- Product
- A substance made.
- Balanced equation
- One with equal numbers of each atom on both sides.
- Displacement
- A more reactive metal taking the place of a less reactive one.
- Reactivity series
- Metals ordered by how readily they react.
Reset break
Part 4 of 24
Pause
That's sitting 1 of 6 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 5 of 24
Learning cycle 1 of 2
Balancing without guesswork
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 6 of 24
Learn
Conservation of mass
The same atoms exist before and after; they have swapped partners. If a reaction appears to lose mass, a gas has escaped; if it appears to gain, a gas from the air has joined in. Nothing has vanished.
Explore the idea
Part 7 of 24
Learn
A reliable balancing method
Never change a subscript — that would change the substance. Only put big numbers in front. Count each element, balance metals first, then non-metals, then hydrogen, then oxygen last. Recount at the end: CH4 + 2O2 → CO2 + 2H2O.
Reset break
Part 8 of 24
Pause
That's sitting 2 of 6 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 9 of 24
Quick check
Part 10 of 24
Learning cycle
Part 11 of 24
Learning cycle 2 of 2
Predicting with the reactivity series
A short piece of teaching, then a check to make sure it has landed.
Reset break
Part 12 of 24
Pause
That's sitting 3 of 6 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 13 of 24
Learn
The reactivity series
Potassium, sodium, calcium, magnesium, aluminium, zinc, iron, copper, silver, gold. Reactivity reflects how readily a metal loses electrons, which is why the top of the list reacts violently with water and the bottom is found as the metal itself.
Explore the idea
Part 14 of 24
Learn
Displacement and extraction
A more reactive metal displaces a less reactive one from its compound: zinc + copper sulfate → zinc sulfate + copper, and the blue solution fades. The same logic explains extraction: metals below carbon can be reduced with carbon, while those above need electrolysis.
Quick check
Part 15 of 24
Reset break
Part 16 of 24
Pause
That's sitting 4 of 6 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 17 of 24
Common mix-ups
Part 18 of 24
Common mix-ups
Things people often get wrong
- Changing a subscript to balance an equation changes the chemical itself.
- Mass appearing to change usually means a gas entered or escaped.
- Gold's rarity is not why it is unreactive — its position in the series is.
Challenge round
Part 19 of 24
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Reset break
Part 20 of 24
Pause
That's sitting 5 of 6 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 21 of 24
Game · Recall cards
Balance: __CH4 + __O2 → CO2 + __H2O
Card 1 of 4
Exit quiz
Part 22 of 24
Exit quiz
Show what you've learned
6 questions, marked together at the end. Nothing is timed.
1. Mass is conserved because atoms are...
2. Balance oxygen...
3. Most reactive listed here:
4. A fading blue solution suggests...
5. Iron is extracted using...
6. Gold is found as the metal because it is...
Mastery quiz
Part 23 of 24
Marked quiz
End of lesson quiz: Balancing equations and the reactivity series
4 questions, marked with the reasoning shown. No timer.
1. Balance: __CH4 + __O2 → CO2 + __H2O
2. To balance you may change only...
3. Which displacement happens?
4. Metals above carbon are extracted by...
Lesson round-up
Part 24 of 24
Lesson round-up
Ready when you are
Quiz score
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Points this lesson
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Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?
Ask LunaPart 1 of 24 · Watch & discover