chemistry revision notes

• acids are solutions that reacts with alkalis, turns litmus paper red and has a pH of lees than 7
• alkalis are solutions that contain excess OH- ions, turns litmus paper blue and has a pH of more than 7
• neutral is a solution that is neither acidic or alkaline and has a pH of 7
• 0-6 acidic
• 7 neutral
• 8-14 alkaline
• yellow/orange/red - acid -the closer to red the stronger the acid
• green - neutral
• blue/purple - alkali - the closer to purple the stronger the alkali
• blue litmus paper turns red under acidic conditions
• red litmus paper turns blue under alkaline conditions
• independent variable - changed
• dependent variable - observed and measured
• controlled variable - kept the same
• chemical change - new substances formed and they are not easily reversed

  signs of chemical change - colour change, temperature change, gas produced, light produced, odour produced, precipitate formed
• physical change - no new substances formed and is easily reversed, often involves a change of state
• endothermic reactions take in energy from the surroundings

  some rections are exothermic because - breaking bonds requires energy, making bonds release energy, more energy is taken in than given out
• exothermic reaction transfers energy to surroundings

  some reactions are exothermic because - breaking bonds requires energy, making bonds releases energy, more energy is given out than taken in
• for a reaction to occur, particles of the reactants must collide with eachother
• rates of reaction will increase if there are more high-energy collisions between particles
• heat energy - unit is J joules
• temperature - units is °C
• 7 stores of energy - thermal, kinetic, chemical potential, gravitational potential, elastic potential