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EnglandCombined Science

Chemistry: Chemical reactions

6 dot points across 6 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How does passing electricity through an ionic compound break it down, and what is made at each electrode?

Electrolysis of molten ionic compounds and aqueous solutions, the movement of ions to the electrodes, the products at the cathode and anode, the rules for aqueous electrolysis, and the use of electrolysis to extract reactive metals.
A focused answer to the OCR Gateway GCSE Combined Science A topic C3 on electrolysis, covering electrolysis of molten and aqueous ionic compounds, ion movement to the electrodes, the products at the cathode and anode, the rules for aqueous solutions, and extracting reactive metals.
9 min answer →

Why do some reactions give out heat and others take it in, and how do we show this on an energy profile?

Exothermic and endothermic reactions and everyday examples, temperature changes in reactions, reaction profile diagrams, activation energy, and the energy change in terms of breaking and making bonds.
A focused answer to the OCR Gateway GCSE Combined Science A topic C3 on energetics, covering exothermic and endothermic reactions and examples, temperature changes, reaction profile diagrams, activation energy, and the energy change explained by breaking and making bonds.
9 min answer →

How can we identify the ions and gases present in a substance using chemical tests?

Tests for the common gases (hydrogen, oxygen, carbon dioxide and chlorine), flame tests for metal ions, tests for carbonate, halide and sulfate ions, and the use of these tests to identify an unknown compound.
A focused answer to the OCR Gateway GCSE Combined Science A topic C4 on identifying substances, covering tests for hydrogen, oxygen, carbon dioxide and chlorine, flame tests for metal ions, and tests for carbonate, halide and sulfate ions to identify an unknown compound.
9 min answer →

How does the reactivity series let us predict displacement reactions and how metals are extracted?

The reactivity series of metals, displacement reactions of metals and their salts, the reactions of metals with water and acids, the extraction of metals by reduction with carbon, and writing ionic and half equations.
A focused answer to the OCR Gateway GCSE Combined Science A topic C4 on predicting reactions, covering the reactivity series, displacement reactions, reactions of metals with water and acids, extraction of metals by reduction with carbon, and writing ionic and half equations.
9 min answer →

What controls the rate of a reaction, what is dynamic equilibrium, and how do we use moles to measure amounts?

The factors affecting the rate of reaction (concentration, temperature, surface area, catalysts) and collision theory, the mole and concentration calculations, reversible reactions and dynamic equilibrium, Le Chatelier's principle, and the Haber process.
A focused answer to the OCR Gateway GCSE Combined Science A topics C5 and C6 on monitoring and controlling reactions, covering the factors affecting rate and collision theory, the mole and concentration calculations, reversible reactions and dynamic equilibrium, and the Haber process.
10 min answer →

What are the main types of chemical reaction, and how do acids and bases react?

Word and balanced symbol equations, conservation of mass, the reactions of acids with metals, bases and carbonates, neutralisation, the pH scale, and oxidation and reduction in terms of oxygen and electrons.
A focused answer to the OCR Gateway GCSE Combined Science A topic C3 on types of reaction, covering word and balanced symbol equations, conservation of mass, reactions of acids with metals, bases and carbonates, neutralisation and the pH scale, and oxidation and reduction.
9 min answer →