Ever wondered how chemists know exactly how much of something...
Chemistry225 views·Updated Jun 4, 2026·3 pagesComprehensive AQA Quantitative Chemistry Revision Notes
Millie@millie_rains
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Chemical Groups and Their Properties
Group 1 metals get more reactive as you go down the periodic table because it becomes easier for larger atoms to lose their outer electron. These metals have lower melting and boiling points as their relative atomic mass (RAM) increases.
When Group 1 metals meet water, they create metal hydroxides and hydrogen gas. Heat them with chlorine gas, and you'll get metal chlorides instead.
Group 7 elements (halogens) work the opposite way - they become less reactive going down the group because larger atoms find it harder to gain electrons. Their melting and boiling points increase with RAM though.
Key Insight: Group 0 (noble gases) have higher boiling points as RAM increases due to stronger intermolecular forces from more electrons.
Bond breaking always requires energy (endothermic), while bond making always releases energy (exothermic). The limiting reactant determines how much product you can make - it's directly proportional to your final amount.
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Essential Definitions and Concepts
Avogadro's constant (6.02 × 10²³) tells you exactly how many particles are in one mole of any substance. Think of it as chemistry's magic number that connects the microscopic world to measurable amounts.
Concentration measures how much substance you've packed into a given volume of solution. The conservation of mass principle is beautifully simple - no atoms disappear or appear from nowhere, so your reactants' mass always equals your products' mass.
The limiting reactant is like the ingredient that runs out first when you're cooking - it completely controls how much product you can make. Other reactants are added in excess, but they can't do anything once the limiting one is gone.
Remember: Relative formula mass equals the mass of one mole of that substance in grams - this connection makes calculations much easier.
Relative formula mass is just the sum of all the relative atomic masses in a compound, giving you a direct link between molecular scale and laboratory scale.
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Quantitative Chemistry in Practice
Conservation of mass means balanced equations aren't just neat - they're essential. No atoms vanish or appear during reactions, making the mass of reactants equal the mass of products every single time.
Sometimes you'll notice mass changes during experiments, but don't panic. If mass increases, a gas was a reactant. If mass decreases, a gas was produced and escaped. The relative formula mass of reactants always equals the relative formula mass of products.
Moles are chemistry's counting unit, measured as mass divided by Mr (or Ar for elements). One mole's mass in grams equals its relative formula mass, thanks to Avogadro's constant.
Pro Tip: The limiting reactant determines your product amount - master this concept and you'll ace stoichiometry problems.
Understanding concentration lets you work with solutions effectively. Remember, the limiting reactant principle means the amount of this reactant directly equals the amount of product you can make.
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Chemistry225 views·Updated Jun 4, 2026·3 pagesComprehensive AQA Quantitative Chemistry Revision Notes
Millie@millie_rains
Ever wondered how chemists know exactly how much of something they've made in a reaction? Quantitative chemistry is all about the maths behind chemical reactions - from calculating masses to understanding why some reactions stop before others. It's the toolkit...
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Chemical Groups and Their Properties
Group 1 metals get more reactive as you go down the periodic table because it becomes easier for larger atoms to lose their outer electron. These metals have lower melting and boiling points as their relative atomic mass (RAM) increases.
When Group 1 metals meet water, they create metal hydroxides and hydrogen gas. Heat them with chlorine gas, and you'll get metal chlorides instead.
Group 7 elements (halogens) work the opposite way - they become less reactive going down the group because larger atoms find it harder to gain electrons. Their melting and boiling points increase with RAM though.
Key Insight: Group 0 (noble gases) have higher boiling points as RAM increases due to stronger intermolecular forces from more electrons.
Bond breaking always requires energy (endothermic), while bond making always releases energy (exothermic). The limiting reactant determines how much product you can make - it's directly proportional to your final amount.
2
of 3Sign up to see the content. It's free!
- Access to all documents
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Essential Definitions and Concepts
Avogadro's constant (6.02 × 10²³) tells you exactly how many particles are in one mole of any substance. Think of it as chemistry's magic number that connects the microscopic world to measurable amounts.
Concentration measures how much substance you've packed into a given volume of solution. The conservation of mass principle is beautifully simple - no atoms disappear or appear from nowhere, so your reactants' mass always equals your products' mass.
The limiting reactant is like the ingredient that runs out first when you're cooking - it completely controls how much product you can make. Other reactants are added in excess, but they can't do anything once the limiting one is gone.
Remember: Relative formula mass equals the mass of one mole of that substance in grams - this connection makes calculations much easier.
Relative formula mass is just the sum of all the relative atomic masses in a compound, giving you a direct link between molecular scale and laboratory scale.
3
of 3Sign up to see the content. It's free!
- Access to all documents
- Improve your grades
- Join milions of students
Quantitative Chemistry in Practice
Conservation of mass means balanced equations aren't just neat - they're essential. No atoms vanish or appear during reactions, making the mass of reactants equal the mass of products every single time.
Sometimes you'll notice mass changes during experiments, but don't panic. If mass increases, a gas was a reactant. If mass decreases, a gas was produced and escaped. The relative formula mass of reactants always equals the relative formula mass of products.
Moles are chemistry's counting unit, measured as mass divided by Mr (or Ar for elements). One mole's mass in grams equals its relative formula mass, thanks to Avogadro's constant.
Pro Tip: The limiting reactant determines your product amount - master this concept and you'll ace stoichiometry problems.
Understanding concentration lets you work with solutions effectively. Remember, the limiting reactant principle means the amount of this reactant directly equals the amount of product you can make.
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: Law of Conservation of Mass
3Most 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