Grade 12 · 🧪 Chemistry · Chemical kinetics
Race fizzing tablets in hot and cold water
Time how long an effervescent tablet takes to dissolve at different temperatures and particle sizes, and plot reaction rate.
Why this matters
Food in a refrigerator spoils more slowly because cold slows chemical reactions. Factories that make cement, fertiliser or medicine control temperature and particle size to make reactions run at exactly the right speed. This experiment measures the same effects with a fizzy tablet.
Watch the demo
Video coming soon
We're recording a demo for this experiment. Until then, follow the step-by-step guide below.
The science
Collision theory
Particles must collide with enough energy (the activation energy) to react. Anything that makes useful collisions more frequent speeds up the reaction.
Factors affecting rate
- Temperature: faster particles collide more often and with more energy.
- Surface area: smaller pieces expose more particles to collisions.
- Concentration: more particles per volume means more collisions.
You'll need
- 4 effervescent tablets↳ Effervescent vitamin C or antacid tablets from a pharmacy
- 3 clear cups
- Cold water (from the fridge), room-temperature water and warm water
- A timer or phone
- A thermometer, if you have one (optional)
Safety first
- Use warm tap water, not boiling water.
- Don't drink the solutions.
Step by step
0/5 doneWhat you should see
The tablet dissolves fastest in warm water and slowest in cold water. The crushed tablet finishes much faster than the whole tablet at the same temperature.
Why it happens
The fizz is carbon dioxide made by an acid–carbonate reaction. In warm water, particles move faster and collide more often with enough energy to react. Crushing the tablet increases its surface area, so more particles can react at once. Both increase the reaction rate, as collision theory predicts.
Didn't work? Try this
The times are very close together.
Make the temperature difference bigger (fridge-cold vs warm), and use the same volume of water each time.
It's hard to tell when fizzing stops.
Stop the timer when the last solid piece disappears instead.
Still stuck? Ask the lab assistant
Check your understanding
1. Why does the tablet react faster in warm water?
2. Crushing the tablet speeds up the reaction because it…
Your lab notebook
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