Chemistry is all around you - from the air you...
Chemistry266 views·Updated 31 Aug 2026·5 pagesAQA Combined Science Chemistry Paper 2: Higher Tier
Faye Findlay@fayefindlay_ylvf
1 / 5
1
of 5
Rate of Reaction & Equilibrium
Ever wondered why some reactions happen instantly whilst others take ages? The rate of reaction measures how quickly reactants transform into products, and it's all about particle collisions.
Collision theory explains that particles must crash into each other with enough energy to create a successful reaction. You can speed things up by increasing temperature (particles move faster), concentration (more particles in the same space), pressure (particles squashed together), or surface area (more exposed reaction sites).
Catalysts are like chemical matchmakers - they speed up reactions without getting used up themselves. Meanwhile, reversible reactions reach equilibrium when the forward and backward reactions happen at the same rate, shown by the ⇌ symbol.
Key Tip: Remember that Le Chatelier's Principle means equilibrium systems always fight back against changes - if you increase pressure, the system shifts to reduce it!
2
of 5
Hydrocarbons & Crude Oil
Hydrocarbons are simple compounds made only of carbon and hydrogen atoms, but they power our entire world! The simplest type, alkanes, follow the formula CnH2n+2 - from methane (CH4) to butane (C4H10).
Crude oil is ancient plankton that's been cooking underground for millions of years. We extract this non-renewable treasure through fractional distillation - heating it up so different compounds evaporate at different temperatures.
Longer hydrocarbon chains are thick and less flammable, whilst shorter ones are runny and highly flammable. That's why we use cracking to split long chains into more useful shorter ones and reactive alkenes.
Remember: In fractional distillation, it's hotter at the bottom (longer hydrocarbons) and cooler at the top (shorter hydrocarbons) - think of it like a chemical skyscraper!
3
of 5
Purity & Chemical Analysis
Pure substances are chemistry's perfectionists - they contain only one compound or element and melt or boil at exact temperatures. But most useful materials are actually formulations - carefully designed mixtures that do specific jobs perfectly.
Chromatography is your detective tool for separating mixtures. It works using a mobile phase (where molecules can move) and a stationary phase (where they can't), letting you identify mystery substances.
You can also identify gases using simple tests: chlorine turns damp litmus paper white, oxygen relights a glowing splint, and carbon dioxide makes limewater go cloudy.
Pro Tip: The further a substance travels in chromatography, the more soluble it is in the mobile phase - use this to identify unknown compounds!
4
of 5
Chemistry of the Atmosphere
Our atmosphere wasn't always perfect for life - it evolved through billions of years of volcanic activity and biological processes. Early volcanoes released water vapour that condensed into oceans, whilst algae and plants gradually pumped out oxygen through photosynthesis.
Greenhouse gases like carbon dioxide, methane, and water vapour act as Earth's insulating blanket. However, human activities including deforestation, burning fossil fuels, and agriculture have dramatically increased these gases.
This creates serious consequences: melting ice caps, changing rainfall patterns, and shifting storm systems. Your carbon footprint measures how much CO2 and other greenhouse gases you're responsible for throughout your lifetime.
Climate Action: Reducing our carbon footprint through renewable energy, efficient processes, and sustainable choices is crucial for our planet's future!
5
of 5
Using Resources Sustainably
Renewable resources can be replaced as fast as we use them, whilst non-renewable resources can't keep up with our demands. Understanding this difference is crucial for managing Earth's precious materials.
Potable water (safe drinking water) requires careful treatment: fresh water passes through filtration systems, then gets sterilised using chlorine, ozone, or UV light. It sounds simple, but clean water is a luxury many lack!
Life cycle assessment tracks a product's environmental impact from raw material extraction through manufacturing, use, and disposal. Sewage treatment involves screening, settling, aerobic treatment of liquid waste, and anaerobic digestion of solid sludge.
Sustainability Matters: Every product you use has hidden environmental costs - thinking about life cycles helps you make smarter choices for the planet!
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Chemistry266 views·Updated 31 Aug 2026·5 pagesAQA Combined Science Chemistry Paper 2: Higher Tier
Faye Findlay@fayefindlay_ylvf
Chemistry is all around you - from the air you breathe to the water you drink! This summary covers the essential reactions, compounds, and processes that shape our world, giving you the knowledge you need to ace your chemistry exams.
1
of 5
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Rate of Reaction & Equilibrium
Ever wondered why some reactions happen instantly whilst others take ages? The rate of reaction measures how quickly reactants transform into products, and it's all about particle collisions.
Collision theory explains that particles must crash into each other with enough energy to create a successful reaction. You can speed things up by increasing temperature (particles move faster), concentration (more particles in the same space), pressure (particles squashed together), or surface area (more exposed reaction sites).
Catalysts are like chemical matchmakers - they speed up reactions without getting used up themselves. Meanwhile, reversible reactions reach equilibrium when the forward and backward reactions happen at the same rate, shown by the ⇌ symbol.
Key Tip: Remember that Le Chatelier's Principle means equilibrium systems always fight back against changes - if you increase pressure, the system shifts to reduce it!
2
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Hydrocarbons & Crude Oil
Hydrocarbons are simple compounds made only of carbon and hydrogen atoms, but they power our entire world! The simplest type, alkanes, follow the formula CnH2n+2 - from methane (CH4) to butane (C4H10).
Crude oil is ancient plankton that's been cooking underground for millions of years. We extract this non-renewable treasure through fractional distillation - heating it up so different compounds evaporate at different temperatures.
Longer hydrocarbon chains are thick and less flammable, whilst shorter ones are runny and highly flammable. That's why we use cracking to split long chains into more useful shorter ones and reactive alkenes.
Remember: In fractional distillation, it's hotter at the bottom (longer hydrocarbons) and cooler at the top (shorter hydrocarbons) - think of it like a chemical skyscraper!
3
of 5Sign up to see the content. It's free!
- Access to all documents
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Purity & Chemical Analysis
Pure substances are chemistry's perfectionists - they contain only one compound or element and melt or boil at exact temperatures. But most useful materials are actually formulations - carefully designed mixtures that do specific jobs perfectly.
Chromatography is your detective tool for separating mixtures. It works using a mobile phase (where molecules can move) and a stationary phase (where they can't), letting you identify mystery substances.
You can also identify gases using simple tests: chlorine turns damp litmus paper white, oxygen relights a glowing splint, and carbon dioxide makes limewater go cloudy.
Pro Tip: The further a substance travels in chromatography, the more soluble it is in the mobile phase - use this to identify unknown compounds!
4
of 5Sign up to see the content. It's free!
- Access to all documents
- Improve your grades
- Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Chemistry of the Atmosphere
Our atmosphere wasn't always perfect for life - it evolved through billions of years of volcanic activity and biological processes. Early volcanoes released water vapour that condensed into oceans, whilst algae and plants gradually pumped out oxygen through photosynthesis.
Greenhouse gases like carbon dioxide, methane, and water vapour act as Earth's insulating blanket. However, human activities including deforestation, burning fossil fuels, and agriculture have dramatically increased these gases.
This creates serious consequences: melting ice caps, changing rainfall patterns, and shifting storm systems. Your carbon footprint measures how much CO2 and other greenhouse gases you're responsible for throughout your lifetime.
Climate Action: Reducing our carbon footprint through renewable energy, efficient processes, and sustainable choices is crucial for our planet's future!
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By signing up you accept Terms of Service and Privacy Policy
Using Resources Sustainably
Renewable resources can be replaced as fast as we use them, whilst non-renewable resources can't keep up with our demands. Understanding this difference is crucial for managing Earth's precious materials.
Potable water (safe drinking water) requires careful treatment: fresh water passes through filtration systems, then gets sterilised using chlorine, ozone, or UV light. It sounds simple, but clean water is a luxury many lack!
Life cycle assessment tracks a product's environmental impact from raw material extraction through manufacturing, use, and disposal. Sewage treatment involves screening, settling, aerobic treatment of liquid waste, and anaerobic digestion of solid sludge.
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We thought you’d never ask...
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.
You can download the app from Google Play Store and Apple App Store.
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Students love us — and so will you.
4.6/5App Store
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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.
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