Chemical reactions (chp.22)

• Chemical reaction is a change that results in the formation of 1 or more new substances.

  HCl+ NaOH-> NaCl +H2O
• Law of conservation of mass

  C6H12O6 +6O2-> 6CO2 + 6H2O + energy(respiration)

  36<-> 36
• In a balanced chemical equation you have the same number of atoms on either side of the equation (reactants -> products) , so the mass on either side must be the same
• The law of conservation of mass states that when a chemical reaction occurs, the total mass of rhe reactants must equal the total mass of the products
• When gases are released from the system we can't measure them on a balance so it can appear as if mass is lost, but it is not
• Exothermic reaction


  Gives out heat energy (burning)
• Endothermic reaction 


  Takes heat energy in (cooking)
• Activation energy 


  Minimum energy required for reactant particles to react with eachother
• Physical change 


  Change of state or shape, no new substances made e.g ripping paper
• Chemical reaction 


  When new substances are made e.g burning paper