Chemical reactions and energy y8

• Exothermic reaction


  Reaction where temperature rises
• Hydrochloric acid reacting with sodium hydroxide solution


  Hydrochloric acid reacting + sodium hydroxide solution –›sodium chloride + water
• Temperature rise


  Means exothermic reaction
• Hydrochloric acid reacting with magnesium


  Hydrochloric acid + magnesium –›magnesium chloride + hydrogen
• Exothermic reactions


  • The temperature goes up
  • The reaction mixture is hotter than its surroundings
  • The mixture gives out heat to air around it
  • The products have less energy than starting materials
• Examples of exothermic reactions


  • Burning/Combustion
  • Neutralization reaction between acids and alkalis
  • Reaction between water and calcium oxide
  • Respiration
• Endothermic reaction


  Reaction where temperature goes down
• Sodium thiosulphate dissolving in water

  Temperature goes down
• Sodium Hydrogen Carbonate reacting with hydrochloric acid


  1. Temperature goes down

  2. The sodium Hydrogen Carbonate fizzes when water is added

  3. The substance produced is carbon dioxide

  4. Test for Carbon Dioxide: bubbles in Limewater –› Cloudy white substance if co² is present

  5. Sodium Hydrogen carbonate + Hydrochloric acid –›Sodium chloride + water
• Endothermic reactions


  • The temperature goes down
  • The reaction mixture is colder than its surroundings
  • The mixture takes in heat from air around it e.g plants
  • The products of reaction have more energy than the starting materials
• Examples of endothermic reactions


  • Photosynthesis
  • Thermal decomposition of limestone
  • Heating blue copper sulphate
• When bonds break, energy is absorbed (endothermic)
• When bonds form, energy is released (exothermic)
• Overall in a reaction there can only be more bonds breaking than forming so overall the reaction is endothermic
• There could be more bonds forming then breaking so a reaction could be exothermic
• Investigating Energy changes when compounds dissolve

  1. Measure 20cm³ of distilled water into a boiling tube

  2. Add 2 spatulas of the solid

  3. Stir gently with the thermometer until the solid dissolves
• Factors that should be kept constant in order to make the practical fair


  • Volume of water used
  • Mass of solid added
  • Time between temperature readings
  • Amount of stirring
• Errors in your experiment
• Fuel


  A substance which reacts with oxygen to give out a large amount of energy; it's oxidized
• Combustion


  The technical term for burning
• Characteristics of a good fuel


  • Burns easily
  • Produces little ash or smokes
  • Produces a large amount of energy when burnt
  • Easily to stove and transport
• Experiment to identify the products of Combustion

  1. The pump is used to draw the gases produced by combustion which are sourced through the apparatus

  2. The ice condense any water vapour to liquid water

  3. Anhydrous copper sulphate turns from white to blue if water is presented

  4. Anhydrous cobalt chloride paper turns from blue to pink if water is present

  5. Lime water turns milky/ cloudy white when carbon dioxide is bubbled through it
• All these fuels produce carbon dioxide co² and water H₂0
• Equation for methane burning


  Methane + oxygen - > Carbon dioxide + water
• Hydrocarbon


  Contains carbon and hydrogen atoms only
• Carbohydrate


  Contains carbon,hydrogen and oxygen atoms
• Energy is obtained from food by respiration
• Carbohydrates such as glucose and starch are a main source of energy
• Respiration


  Glucose + Oxygen -> Carbon dioxide + water (exothermic)
• Photosynthesis


  Carbon dioxide + water - > Glucose + oxygen (endothermic)