C3 - chemical reactions

• avogadro's constant is the number of particles in 1 mole of any substance. it is 6.02 x 10^23
• 1 mole is the amount of substance that contains the same number of particles as there are atoms in 12g of carbon-12
• hydrogen is a colourless gas

  if its present in a test tube, a lighted splint will ignite with a squeaky pop
• oxygen is a colourless gas

  if it's present in a test tube, a glowing splint wil relight when held inside
• carbon dioxide is a colourless gas

  if it's bubbled through limewater, the limewater will turn milky/cloudy
• chlorine is a poisonous green gas

  it's present if damp litmus paper turns white
• the law of conservation of mass states that the total mass of the products is equal to the total mass of the reactants
• endothermic reaction is a reaction that takes in energy from the surroundings

  e.g. photosynthesis
• exothermic reaction is a reaction that releases energy to the surroundings

  e.g. combustion
• activation energy is the minimum amount of energy needed to start a reaction
• oxidation is loss of electrons
• reduction is gain of electrons
• oxidising agent is a substance in a redox chemical reaction that gains an electron from a reducing agent
• a reducing agent is a substance that donates electrons to a substance that accepts electrons
• acids form hydrogen ions when they are dissolved in water
• solutions of alkalis contain hydroxide ions
• neutralization equation is H+ + OH- -> H2O
• number of moles = mass / Mr
• sulfate = SO4^2-

  nitrate= NO3-

  carbonate= CO3^2-

  hydroxide= OH

  ammonium= NH4^+

  phosphate= PO4^3-
• energy change= bonds broken- bonds made
• metal carbonate + acid -> salt + water + carbon dioxide
• acid + metal -> salt + hydrogen
• acid + metal base -> salt + water
• acid + metal hydroxide -> salt + water
• acid + metal oxide -> salt + water
• concentration = mass of solute (g) / volume of solution in dm^3
• PANIC stands for positive anode, negative is cathode
• OILRIG stands for oxidation is loss, reduction is gain (of electrons)
• sulfuric acid (H2SO4).
• hydrochloric acid (HCl)
•  nitric acid (HNO3)
• If the reaction flask is closed and no other substance can enter or leave the system, then the total mass of the reaction flask will remain constant

  
  

  This can be demonstrated using many reactions including precipitation reactions, in which two solutions react to form an insoluble solid called a precipitate
• CHANGES IN MASS:

  If the reaction flask is open (a non-enclosed system) and a gaseous product is allowed to escape, then the total mass of the reaction flask will decrease as product mass is lost when the gas particle leaves the system
• when acids are added to water, they form postively charged H+ ions --> this makes the solution acidic
• when alkalis are added to water, the form negatively charged hydroxide ions OH- --> this makes the solution alkali
• on the pH scale, all acids have a pH <7, all alkalis have a pH >7
• the lower the pH, the more acidic it is
• the higher the pH, the more alkaline it is
• pH of 7 = neutral
• pH can be measured using a:

  • universal indicator --> only precise to one whole number
  • digital pH meter --> precise to 2 d.p.