chemical reactions

• When energy is given out, the reaction is EXOTHERMIC
• • When energy is taken in, the reaction is ENDOTHERMIC
• In a physical change, the substances present remain chemically the same; no new substances are formed
• Physical changes are often easy to reverse. Any mixtures produced are usually easy to separate
• • Synthesis occurs when two or more substances react together to form just one product, heat is required to start the reaction but once started,it continues exothermic
• • Decomposition have just one reactant that breaks down to give two or more simpler substances, these reactions are endothermic.They require heat energy. Decomposition caused by heat energy is called thermal decomposition, can also be caused by light energy
• • Neutralisation when acids react with bases or alkalis and salt is produced
• • Precipitation the sudden formation of a solid, either when two solutions are mixed or when a gas is bubbled into a solution.
• 1. Displacement reactions -  A displacement reaction occurs because a more reactive element will displace a less reactive one from a solution of one of its compounds.
• • Combustion The reaction of a substance with oxygen causing the release of energy; it is exothermic and often involves a flame.
• Burning is a combustion in which a flame is produced.
• • Oxidation when a substance gains oxygen during a reaction. We say, it is oxidised.
• • Reduction If a substance loses oxygen during a reaction, it is reduced.
• Reducing agent is an element or compound that will remove oxygen from the other substances.
• Oxidising agent is a substance that will add oxygen to another substance.
• Electrolysis: the breakdown of an ionic compound, molten or in aqueous solution, by the use of electricity
• • Electrolytes: liquids that conduct electricity by the movement of ions (molten or aqueous solutions conduct because they have delocalized or moving electrons, solid ionic compounds can’t)
• • Electrodes: rods in an electrolytic cell which carry the current into and out of the solution. Usually made up of graphite or platinum
• Cathode: negative electrodes
• • Anode: positive electrodes
• • Electroplating: coating a metal with another metal