Chemistry

• hydrated means it has water molecules built into the structure
• anhydrous means no water is present
• a reversible reaction means that the products can react to form the original reactants
• in a closed system , a reversible reaction reaches a state of dynamic equilibrium
• the term dynamic equilibrium usually is shortened to equilibrium
• a reversible reaction always reaches equilibrium in a closed system
• An increase in temperature will let the equilibrium shift to favor the reaction which will reduce the temperature, and the endothermic reaction is forwards
• A decrease in pressure will cause an exothermic reaction to go backwards because it favors the forward direction.
• Increasing the concentration of either product or reactant increases the rate of the reverse reaction
• The position of equilibrium depends on the conditions under which the reaction takes place
• Increasing the concentration of one or more reactant(s) shifts the equilibrium towards the formation of product(s)
• Le Chatelier's principle states that if any change occurs at constant volume and pressure, then the equilibrium shifts so that the effect of the change is minimized
• Le Chatelier's principle states that if any change occurs at constant temperature, then the equilibrium shifts so as to counteract the effect of the change
• If we add a catalyst, there's no change in the position of equilibrium but the speed at which the reaction occurs changes
• the equilibrium will shift to favor a decrease in pressure ( smaller gas molecules)
• the equilibrium will shift to favor an increase in pressure ( higher numbers of gas molecules)
• the equilibrium will shift in the direction of the reaction that uses the reactants, the forward reaction will be favoured
• the forward reaction is also favoured when the concentration of the product is decreased
• the equilibrium will shift in the direction of the reaction that produces the reactants, the reverse reaction is forward
• the reverse reaction is also favoured when the concentration of the product is increased
• concentration moves from the higher concentration to lower concentration
• when there are more products than reactants, the equilibrium lies on the right hand side
• if the concentrations of both reactants and products are equal, then the equilibrium lies exactly in the middle
• Reversible reaction


  A chemical reaction that can go either forwards or backwards depending on the conditions
• Reversible reaction


  • Nitrogen + hydrogen = ammonia

  N2(g) + 3H2(g) ⇌ 2NH3(g)
• Reversible hydration of salts

  Thermal decomposition of salts (any hydrated salts) results in dehydration

  Dehydration reaction can be reversed slowly by adding water
• Dynamic equilibrium


  In a closed system, a reversible reaction reaches a state where the forward and back reactions take place at the same rate
• Increase in temperature


  Equilibrium shifts to favour the endothermic reaction
• Decrease in temperature


  Equilibrium shifts to favour the exothermic reaction
• Increase in pressure


  Equilibrium shifts to favour a decrease in pressure
• Decrease in pressure


  Equilibrium shifts to favour an increase in pressure
• Catalyst in Haber process

  • Ensures the reaction is fast enough for a dynamic equilibrium to be set up
• Typical conditions in Haber process


  • N2 and H2 mixed in 1:3 ratio

  Optimum temperature of 450°C

  Pressure of 20,000 kPa (200 ATM)

  Catalyst of finely divided iron
• Fertiliser


  A natural or artificial substance containing chemical elements (such as Nitrogen (N), Phosphorus (P) and Potassium (K)) that improve growth and productiveness of plants
• Combustion


  A chemical process in which a substance reacts rapidly with oxygen and gives off heat
• Oxidation


  A chemical change that involves the transfer of electrons or oxygen among atoms
• Reduction


  The gain of electrons, loss of oxygen, or gain of hydrogen
• Usual oxidation states of elements

  • Hydrogen (H): +I

  Sodium (Na) and other group I metals: +I

  Calcium (Ca) and other group II metals: +II

  Aluminium (Al): +III

  Chlorine (Cl) and other group VII non-metals, in compounds without oxygen: -I

  Oxygen (O2) [except in peroxides]: -II

  Iron (Fe): +II & +III

  Copper (Cu): +I & +II

  Manganese (Mn): +II, +IV & +VII

  Chromium (Cr): +III & VI
• Acid


  A chemical substance, usually a liquid, which contains hydrogen and can react with other substances to form salts
• Base


  Substances that react with acids and neutralise them. They are usually metal oxides, metal hydroxides, metal carbonates or metal hydrogen carbonates