Spoots

• Signs of a chemical reaction

  • Change of colour
  • Energy change
  • Precipitate forming
  • Effervescence
• In all chemical reactions new substances are produced
• Examples of everyday chemical reactions

  • Fast
  • Slow
• Everything is made from approximately 100 elements
• Each element has a name and a symbol
• Mixture


  Two or more substances come together without reacting
• In a mixture the elements retain their physical and chemical identity
• Compound


  New substance formed when two or more elements are chemically bonded together
• A new compound has completely new chemical and physical properties
• Methods to break down chemical compounds

  1. Heat alone

  2. Heating with carbon

  3. Electrolysis
• Composition of air
• Tests for common gases

  1. Oxygen relights a glowing splint

  2. Hydrogen burns with a squeaky pop

  3. Carbon dioxide turns limewater cloudy
• Processes that contribute to climate change

  Increased levels of carbon dioxide can trap Earth's heat leading to temperature increase
• Mixtures can be separated using physical methods, compounds can only be separated into elements using chemical methods
• Electrolysis


  Uses electricity to separate a compound into its elements
• Using heat to break down compounds

  Heating metal oxides with carbon can break them down into metal and oxygen
• Word equation


  Describes a chemical reaction using reactants and products
• Composition of air


  • Nitrogen (78%)
  • Oxygen (21%)
  • Carbon dioxide (0.03%)
  • Argon (0.9%)
  • Other gases (tiny percentage)
• Gas tests


  1. Oxygen relights a glowing splint

  2. Hydrogen burns with a squeaky pop

  3. Carbon dioxide turns limewater cloudy
• The carbon cycle


  1. Plants use carbon dioxide and sunlight to grow

  2. Fossil fuels made from buried plants

  3. Burning fossil fuels releases carbon dioxide

  
• Changes in the carbon cycle


  Can alter the natural balance of gases in the atmosphere and result in climate change
• A chemical reaction occurs when two or more substances (reactants) undergo a change whereby new products are created
• Reaction rate


  Can be measured as rate of formation of product or rate of disappearance of reactant
• Examples of everyday chemical reactions and their rates

  • Burning petrol in engine (fast)
  • Milk turning sour (slow)
  • Making wine from grapes (slow)
• A chemical word equation does not tell you about the speed of the reaction, the reaction conditions or the energy changes involved
• Activation energy


  Minimum energy required for a reaction to occur between molecules
• Ways to increase the rate of a chemical reaction

  1. Increase the number of collisions

  2. Reduce the energy needed for the reaction to take place
• Particle size


  • Increasing the effective reaction surface area by reducing particle size increases the reaction rate
• Increasing the surface area of a reactant


  Increases the rate of a reaction
• Increasing the temperature of reactants

  Increases the rate of reaction
• Increasing the concentration of reactants

  Increases the rate of reaction
• Increasing the pressure of a gas

  Increases the concentration of reactant gas molecules and increases the reaction rate
• Catalyst


  A substance that speeds up or slows down a chemical reaction without being consumed or altered itself
• When the temperature is increased


  The rate of reaction increases
• Concentration


  The greater the concentration, the more reactant molecules will be present per unit volume of the material
• Greater concentration of reactants


  Increases the chance for collisions to take place between reactant molecules so the reaction rate will increase
• If a gas is compressed into a smaller volume

  Its pressure will increase and this will have the effect of increasing the concentration of the reactant gas molecules, therefore increasing the reaction rate
• Catalyst


  A chemical which makes a reaction go faster but remains unchanged after the reaction
• Catalysts


  • They take part in a chemical reaction, but do not get used up and can be reused with more reactants
  • They are chemically the same at the end of the reaction
• Common catalysts and their uses

  • Nickel - Making margarine from vegetable oils
  • Vanadium pentoxide - Manufacture of sulphuric acid
  • Enzymes - Various chemical changes in our bodies
  • Iron - Manufacture of ammonia
  • Platinum - Manufacture of nitric acid