GCSE Chemistry AQA Paper 2 Mind Maps

Earth's Atmosphere and Climate Change

Ever wondered why Earth isn't a frozen wasteland like Mars? It's all down to our atmospheric composition and the greenhouse effect that keeps us cosy.

Today's atmosphere is 78% nitrogen and 21% oxygen, but 4.6 billion years ago, Earth was completely different. The early atmosphere was mainly carbon dioxide with no oxygen - just like Mars and Venus today. Intense volcanic activity released gases, and as water vapour cooled to form oceans, CO₂ dissolved and reacted with minerals.

Fossil fuels formed when ancient organic matter got buried and compressed. Coal came from ferns and trees, whilst oil and gas formed from compressed plankton. The greenhouse effect works because energy from the sun arrives as short wavelength radiation, gets absorbed by Earth's surface, then radiates back as long wavelength radiation that greenhouse gases trap.

Key Insight: Your carbon footprint measures all the CO₂ and greenhouse gases produced throughout a product's entire lifecycle - not just when you use it.

Climate change happens as we burn fossil fuels, releasing more CO₂ and methane. This increases temperatures, melts polar ice, raises sea levels, and creates more extreme weather patterns.

Crude Oil and Organic Chemistry

Crude oil might look like black gunk, but it's actually a treasure trove of useful hydrocarbons - molecules made only of hydrogen and carbon atoms.

Fractional distillation separates crude oil based on three key properties: volatility (how easily substances turn to gas), viscosity (thickness), and flammability. Short-chain hydrocarbons are more volatile, less viscous, and more flammable than long chains.

Alkanes follow the formula CₙH₂ₙ₊₂ and are saturated (no double bonds). Think methane, ethane, propane - you'll recognise these from camping gas! Cracking breaks long-chain hydrocarbons into shorter, more useful ones, often producing alkenes (CₙH₂ₙ) with C=C double bonds.

Remember: The functional group determines how a molecule behaves - it's like a chemical personality trait.

Alcohols contain the -OH group and can be made by fermentation (yeast + glucose at 30°C) or reacting alkenes with steam. Carboxylic acids have the -COOH group and are weak acids. When alcohols react with carboxylic acids, they form esters - the sweet-smelling compounds in perfumes.

Polymers form when thousands of small monomers join together. Addition polymers come from alkenes, whilst condensation polymers form when molecules react and lose small molecules like water.

Rates of Reactions and Equilibrium

Chemical reactions are like busy dance floors - particles need to collide with enough energy to actually react, and several factors control how often this happens.

Collision theory explains that reactions only occur when particles collide with sufficient energy to overcome the activation energy barrier. Think of it like needing enough speed to jump over a fence - too slow and you'll crash into it.

The rate of reaction depends on temperature, concentration, surface area, and catalysts. Higher temperatures make particles move faster, increasing successful collisions. Higher concentrations mean more particles bumping into each other. Breaking solids into smaller pieces increases surface area, giving more space for collisions.

Pro Tip: Catalysts are like chemical cheat codes - they lower the activation energy needed, speeding up reactions without getting used up.

In reversible reactions, products can turn back into reactants. In a closed system, you'll reach equilibrium when forward and reverse reactions happen at the same rate. Le Chatelier's principle states that if you change conditions, the equilibrium shifts to counteract that change - it's nature's way of fighting back!

If you increase temperature, equilibrium moves towards the endothermic direction to absorb that extra heat. Increase pressure, and equilibrium shifts towards the side with fewer gas molecules.

Chemical Analysis and Testing

Real-world chemistry isn't just about theory - you need to identify what substances you're actually dealing with, and there are loads of clever ways to do this.

A pure substance has a fixed melting and boiling point, whilst formulations are complex mixtures designed for specific purposes like paints, medicines, and fuels. Paper chromatography separates substances based on different solubilities - the Rf value (distance moved by substance ÷ distance moved by solvent) helps identify unknown compounds.

Gas tests are your go-to for identifying common gases. The squeaky pop test detects hydrogen, a glowing splint relights with oxygen, limewater turns cloudy with carbon dioxide, and chlorine bleaches litmus paper white.

Quick Check: Instrumental methods like spectroscopy are faster, more sensitive, and work with tiny samples - perfect for forensic work!

Metal ion tests using sodium hydroxide create coloured precipitates: calcium and magnesium give white, copper(II) gives blue, iron(II) gives green, and iron(III) gives brown. Flame tests show lithium as crimson, sodium as yellow, and potassium as lilac.

For non-metal ions, add dilute acid to carbonates (fizzing = CO₂), use silver nitrate for halides (white = chloride, cream = bromide, yellow = iodide), and barium chloride gives a white precipitate with sulfates.

Resources and Sustainability

The stuff we use every day comes from somewhere, and understanding the difference between finite and renewable resources is crucial for our planet's future.

Finite resources like fossil fuels can't be replaced as quickly as we use them, whilst renewable resources like wood can be replenished. Potable water (safe to drink, not pure) requires filtering and sterilising. Desalination through distillation or reverse osmosis makes seawater drinkable but needs loads of energy.

Corrosion destroys materials through chemical reactions - rusting is iron's biggest enemy. Galvanising (coating with zinc) and sacrificial protection use more reactive metals to prevent corrosion. Alloys like bronze (copper + tin) and steel varieties combine metals for specific properties.

Think Sustainable: Life cycle assessment evaluates a product's environmental impact from cradle to grave - not just how you use it.

Copper extraction from low-grade ores uses phytomining (growing plants that absorb metals) or bioleaching (bacteria that extract metals). The Haber process produces ammonia for NPK fertilisers containing nitrogen, phosphorus, and potassium compounds.

Polymers create environmental challenges - thermosoftening plastics can be reshaped when heated, whilst thermosetting plastics don't melt. Composites combine different materials for enhanced properties, like carbon fibre reinforcement in a polymer matrix.