Chemical calculations might seem intimidating, but they're actually just about...
Chemistry326 views·Updated Jun 11, 2026·2 pagesMaster Chemistry Triple GCSE: Chemical Calculations with Mass
I
isaac@isaac_pcpe
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Conservation of Mass and Apparent Mass Changes
Here's something that might blow your mind: atoms can never be created or destroyed during chemical reactions - they just get shuffled around like pieces in a jigsaw puzzle! This is called the conservation of mass, and it means the total mass before a reaction should equal the total mass after.
But wait - sometimes your scales might tell a different story. If you're doing a reaction and the mass seems to decrease, don't panic! This usually happens when one of your reactants is a gas that escapes into the air.
Take sodium reacting with chlorine gas to make salt (sodium chloride). Your sodium starts off light, but the final salt weighs more because invisible chlorine atoms from the air have joined the party. It's like watching a dance where invisible partners suddenly become visible!
Key Tip: If mass appears to change, look for gases entering or leaving the reaction - they're the usual suspects!
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Excess and Limiting Reactants
Imagine making sandwiches with 10 slices of bread but only 3 slices of cheese - you'll run out of cheese first! Chemical reactions work exactly the same way. The limiting reactant is like your cheese - it runs out first and stops the whole reaction. The excess reactant is your leftover bread.
To figure out which is which, you need to play detective with a simple 5-step process. Start by writing your balanced symbol equation, then pick one reactant and use the equation's ratio to calculate how much of the other reactant you actually need.
The magic happens when you compare what you need versus what you've got. If you need 5g but have 8g, that reactant is in excess. The one that doesn't have enough becomes your limiting reactant - and that's what determines how much product you'll make.
Remember: The limiting reactant is like the bottleneck in your reaction - it controls everything!
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Chemistry326 views·Updated Jun 11, 2026·2 pagesMaster Chemistry Triple GCSE: Chemical Calculations with Mass
I
isaac@isaac_pcpe
Chemical calculations might seem intimidating, but they're actually just about keeping track of atoms and making sure everything adds up correctly. Understanding how mass works in reactions and identifying which chemicals run out first are essential skills that'll pop up...
1
of 2
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Conservation of Mass and Apparent Mass Changes
Here's something that might blow your mind: atoms can never be created or destroyed during chemical reactions - they just get shuffled around like pieces in a jigsaw puzzle! This is called the conservation of mass, and it means the total mass before a reaction should equal the total mass after.
But wait - sometimes your scales might tell a different story. If you're doing a reaction and the mass seems to decrease, don't panic! This usually happens when one of your reactants is a gas that escapes into the air.
Take sodium reacting with chlorine gas to make salt (sodium chloride). Your sodium starts off light, but the final salt weighs more because invisible chlorine atoms from the air have joined the party. It's like watching a dance where invisible partners suddenly become visible!
Key Tip: If mass appears to change, look for gases entering or leaving the reaction - they're the usual suspects!
2
of 2Sign up to see the content. It's free!
- Access to all documents
- Improve your grades
- Join milions of students
Excess and Limiting Reactants
Imagine making sandwiches with 10 slices of bread but only 3 slices of cheese - you'll run out of cheese first! Chemical reactions work exactly the same way. The limiting reactant is like your cheese - it runs out first and stops the whole reaction. The excess reactant is your leftover bread.
To figure out which is which, you need to play detective with a simple 5-step process. Start by writing your balanced symbol equation, then pick one reactant and use the equation's ratio to calculate how much of the other reactant you actually need.
The magic happens when you compare what you need versus what you've got. If you need 5g but have 8g, that reactant is in excess. The one that doesn't have enough becomes your limiting reactant - and that's what determines how much product you'll make.
Remember: The limiting reactant is like the bottleneck in your reaction - it controls everything!
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
Most popular content in Chemistry
9Most popular content
9Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.6/5App Store
4.7/5Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan SiOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha KlichAndroid user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
AnnaiOS user