GCSE/iGCSE Chemistry - Year 1 Week 1
Why Can You Smell Dinner From Upstairs?
States of Matter
Throughout the course, you will be given questions to answer, journal prompts, famous scientists, and practicals to make notes on. You can use a digital journal, a nice physical book or use the journal sheets below.
Big Question
"Why can you smell dinner cooking from another room — even before you can see any steam or smoke?"
Predict
Before we dig in, jot down whether you think each of these is true or false. No peeking ahead, we’ll come back to these at the end.
1. Smell particles travel in a straight line, straight toward your nose, like a beam of light.
2. If the kitchen were warmer, the smell would reach you faster.
Story of the Week
Imagine you’re doing homework upstairs when someone opens the oven downstairs. A minute later, bread.
You didn’t see anything move. Nothing visibly travelled up the stairs. And yet, somehow, information about what’s cooking has arrived at your nose, two floors away. That “somehow” is one of the oldest and best pieces of evidence that matter isn’t as solid and continuous as it looks.
Everything around you, the air in this room, the water in a glass, the metal in a spoon, is made of tiny particles in constant motion, and this week is about what that motion actually looks like, and why it explains everything from smelling toast to why ice melts.
Video Session One
Things to look out for:
How the particle arrangement, movement, and energy differ between solid, liquid, and gas — you’ll need all three for this week’s practice questions.
The correct names for every change of state (there are six, not just “melting” and “freezing”, don’t let condensing and subliming slip past you).
What’s actually changing when a substance changes state. It’s the arrangement and energy of the particles, never the particles themselves.
Video Session Two
Things to look out for:
The precise definition of diffusion.
Why diffusion happens faster in gases than in liquids, and barely happens at all in solids.
The link between temperature and the speed of diffusion — this is the one your Session One video didn’t cover, and it’s exactly what this week’s Big Question hinges on.
⚠ Misconception Alert
A lot of students picture heating a substance as making the particles get bigger, like a balloon inflating. They don’t. Heat a solid, a liquid, or a gas and the particles themselves stay exactly the same size the whole time.
What changes is how fast they’re moving and how far apart they are. Size of particles never changes. Speed and spacing of particles: that’s the whole story.
This is a good place to take a break.
Reading Assignment
This week’s booklet readings: 1 & 2
Hands-On Activity
Diffusion race. You’ll need two clear glasses, hot water, cold water, and food colouring (or a teabag).
1. Fill one glass with hot water and one with cold water (same amount in each).
2. At the same moment, add one drop of food colouring to each glass — don’t stir.
3. Watch both glasses and time how long it takes for the colour to spread evenly through each one.
4. Record your results: which glass finished first, and by roughly how much?
Journal prompt
Using particle theory, explain why one glass diffused faster than the other.
What does this tell you about the relationship between temperature and particle speed?
Watch the Food Colouring Diffusion video by Science fix.
Why not have some fun with diffusion and try the Skittles diffusion experiment?
The Brilliant Mistake
For about a hundred years, some of the smartest chemists in the world believed heat was a substance. They called it “caloric”, an invisible, weightless fluid that flowed from hot objects into cold ones. It was a genuinely useful theory and it explained why a hot cup of tea cools down (caloric flowing out) and why rubbing your hands together warms them up (friction squeezing caloric out of the material).
Antoine Lavoisier, the same chemist who would go on to demolish an entirely different wrong theory about burning, believed in caloric his whole life. It was that convincing. Then, in 1798, a scientist named Benjamin Thompson (later known as Count Rumford) was supervising the boring of cannon barrels at a Munich arsenal. The metal-on-metal friction generated an enormous, continuous
amount of heat, so much that the metal shavings could boil water. If heat were a fluid stored inside the metal, Rumford reasoned, it should eventually run out, the way water drains from a tank. He kept the cannon boring for
hours. The heat never stopped coming. There was no reservoir of caloric hidden inside the cannon barrel large enough to explain that much heat,
endlessly. Rumford proposed something radical instead, that heat wasn’t a substance being released at all. It was motion, the friction was making the particles of the metal vibrate faster, and that vibration was the heat.
Most chemists at the time weren’t convinced — Rumford’s idea sat for decades before kinetic theory (the particle picture you just watched in Session One) finally won out. But he’d correctly identified, using nothing but
a very patient experiment and a lot of cannon barrels, the exact thing you now know as fact: temperature isn’t a fluid moving between objects. It’s how fast the particles inside something are jiggling around.
Scientist Portrait
Robert Boyle (1627–1691) is often called the father of modern chemistry, and the states-of-matter story is a good place to meet him. In an age when most people studying matter were alchemists chasing gold, Boyle argued that everything was made of tiny moving particles (“corpuscles”), and that the physical behaviour of a substance — solid, liquid, gas, how it mixed, how it reacted — came down to how those particles were arranged
and moving. That’s the particle model you used all week, over 350 years before
it had a GCSE spec code.
Add a picture of Robert Boyle to your Scientist Journal and write a few sentences about him.
Return to Predictions
Time to check your answers from the top of the post.
1. Smell particles travel in a straight line, straight toward your nose, like a beam of light. — False. Particles in a gas move randomly, constantly colliding with each other and with air molecules. Diffusion is the net drift from high to low concentration, not a targeted beam.
2. If the kitchen were warmer, the smell would reach you faster. — True. Higher temperature means faster- moving particles, which means faster diffusion.
✅ Big Question — Final Answer
Write a paragrph answering this week's big question. A good answer should mention temperature, kinetic energy, particle movement and diffusion.
10 Practice Questions
1. Name the three states of matter.
2. Describe the arrangement of particles in a solid.
3. Describe the arrangement of particles in a gas.
4. Name the change of state when a liquid turns into a gas.
5. Name the change of state when a gas turns directly into a solid.
6. Explain, in terms of particles, why gases can be compressed but solids cannot.
7. Define diffusion.
8. Explain why diffusion happens faster in a gas than in a liquid.
9. A student heats a solid until it melts. Explain what happens to the particles themselves during this process?
10. Using ideas about particle speed, explain why perfume sprayed in a warm room can be smelled sooner than the same amount sprayed in a cold room.
☑ Checklist
Watched both videos
Completed both booklet readings
Done the diffusion race practical and answered the journal prompt
Answered all 10 practice questions
Can explain diffusion in your own words, using the word “particles”
Next Week Preview
Next week we leave pure substances behind and start mixing things, literally. We’ll look at how to tell an element, a compound, and a mixture apart, and how chemists separate mixtures back out again using everything from filter paper to chromatography.
