chemical changes

• the reactants are the starting materials that undergo change during a chemical reaction
• conservation of mass means that no atoms during a chemical reaction or a change of state are gained or lost and the mass is the same
• relative formula mass is the sum of the relative atomic masses of the atoms in a formula unit
• when a metal reacts with oxygen it forms a metal oxide
• gaining oxygen is called an oxidation reaction
• `the reactivity of a metal depends on its ability to lose electrons an become an ion
• metal displacement reactions occur when a more reactive metal replaces a less reactive metal from a compound
• reactivity series - a table showing how easily different elements can gain or lose electrons
• all acids contain hydrogen
• when acids react with metals they make a salt and a hydrogen gas
• hydrochloric acid makes salts that end in chloride
• sulfuric acid makes salts that end in sulfate
• exothermic reactions transfers energy to the surroundings so the surrounding temperature increases
• an endothermic reaction takes energy from the surroundings so the temp decreases
• chemical reactions can only occur when particles collide with each other and with sufficient energy
• reaction profiles show the relative energies of reactants and products
• bases neutralise acids and form a salt and water
• alkalis are bases that are soluble in water and can neutralise acids
• in an aqueous solution acids produce hydrogen ions
• reduction is gain of electrons
• oxidation is loss of electrons
• when metals react with acids the metal is oxidised
• hydrogen and electrons make hydrogen gas
• salts contain positive ions from the metal and negative ions from the acid.
• acids and metal carbonates make salts water and carbon dioxide
• redox reactions – this means that one substance is reduced and another substance is oxidised
• Acids are neutralised by alkalis (e.g soluble metal hydroxides) and bases (e.g insoluble metal hydroxides and metal oxides) to produce salts and water
• acids are neutralised by metal carbonates to produce salts, water and carbon dioxide
• the charges on the positive ion from the base/alkali/carbonate and the negative ion from the acid must add up to zero.
• oxidation is loss reduction is gain of electrons
• a more reactive elements will displace a less reactive one
• In aqueous solutions acids produce hydrogen ions
• Bases are a chemical that neutralises acids
• A solution with pH below 7 is an acidic solution
• alkalis have a ph of 8-14
• an acid and an alkali together make water, this is neutralisation
• when a metal reacts with oxygen in makes a metal oxide
• metals get oxidised when they react with oxygen in the air.
• in aqueous solutions alkalis produce hydroxide ions
• acids and metal makes water and salt