chemical reactions

• A chemical reaction is a change in which atoms are rearranged to create new substances. The atoms are joined in one way before the reaction and in a different way after the reaction.
• All chemical reactions:

  • Make new substances
  • Transfer energy to or from the surroundings
• We'll know that a chemical reaction occurs if we can observe any of these

  • change of temperatures
  • change of smell/ smell
  • change of colour
  • fizzing
  • observing flames
• Most chemical reactions are not easily reversible. At the end of the reaction it is very difficult to get back the substances you started with.
• Change of state is not a chemical reaction because we're not rearranging the atoms of the substance, their state is the only thing that changes. Change of state is easily reversible as well.
• For a chemical reaction, products look different from the reactants. (the way the substance looks like, and the way it's written)
• An exothermic reaction releases energy in a form of heat to the surroundings.
• An endothermic reaction absorbs energy in a form of heat from the surroundings.
• Respitation, combustion, burning sugar, formation of salt are examples of exothermic reaction
• photosynthesis, cooking are examples of endothermic reaction
• chemical reactions transfer energy that can be useful
• catalysts speed up the rate of chemical reactions without going through a chemical change
• A hazard is a possible source of danger
• Risk is the chance of damage or injury from a hazard
• Burning magnesium has two hazards:

  1. The bright flame could be harmful to eyesight.
  2. The flame is difficult to put out.
• Reactants are always on the left, and products are always on the right.
• Non metals' names change. The metal substances stay the same.
• Sodium bicarbonate = Sodium + Hydrogen + Oxygen + Carbon
• Fossil fuels are dead remains of plants and animals under a massive pressure and weights.
• Fuels go under chemical reactions called conbustion.

  CH4 + O2 -> CO2 + H2O
• Decomposition reaction is when a compound breaks down into simpler compounds or elements.
• Thermal decomposition is when a substance breaks down on heating.
• Metal carbonate -> Metal oxide + Carbon dioxid
• Magnesium + Chlorine -> Magnesium Chloride + Hydrogen
• Magnesium + Hydrochloric acid -> Magnesium Chloride + Hyrdogen
• Magnesium + Sulfuric acid -> Magnesium Sulfate + Hydrogen
• Sodium + Nitric Acid -> Sodium Nitrate + Hydrogen
• Discrete variable is described by words, or by numbers that can only have certain values. (e.g. shoe sizes)