Chemistry265 views·Updated 29 Jun 2026·5 pages

AQA Combined Science Chemistry Paper 2: Higher Tier

Faye Findlay@fayefindlay_ylvf

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Chemistry is all around you - from the air you...

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# Rate of Reaction
The rate of a chemical reaction is how fast the reactants turn into products

# Collision Theory
- mass collision
- faste

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!

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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!

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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!

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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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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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Chemistry265 views·Updated 29 Jun 2026·5 pages

AQA Combined Science Chemistry Paper 2: Higher Tier

Faye Findlay@fayefindlay_ylvf

Add to Google sources

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.

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.

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!

of 5

Hydrocarbons & Crude Oil

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!

of 5

Purity & Chemical Analysis

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!

of 5

Chemistry of the Atmosphere

Climate Action: Reducing our carbon footprint through renewable energy, efficient processes, and sustainable choices is crucial for our planet's future!

of 5

Using Resources Sustainably

Sustainability Matters: Every product you use has hidden environmental costs - thinking about life cycles helps you make smarter choices for the planet!