C7

• Endothermic reaction


  A chemical reaction that absorbs heat energy from its surroundings, causing the reaction vessel to feel cold.
• Thermal Decomposition


  The breakdown of a substance into simpler components using heat energy, examples include calcium carbonate decomposing into calcium oxide and carbon dioxide at high temperatures.
• Photosynthesis


  The process by which plants produce glucose and oxygen from carbon dioxide and water, using energy from sunlight.
• Electrolysis


  The process of using electricity to drive a chemical reaction, such as the decomposition of water into hydrogen and oxygen.
• Activation Energy


  The energy required to break the bonds in the reactants and complete the reaction.
• Exothermic Reaction


  A chemical reaction that releases heat energy to its surroundings, causing the reaction vessel to feel warm or hot when touched.
• Exothermic vs. Endothermic Reactions

  Bond breaking (reactants) is often endothermic, requiring energy input. Bond forming (products) is often exothermic, releasing energy. The overall reaction type (exo or endo) depends on the total energy change, influenced by the types of bonds broken and formed.
• Definition of Endothermic Reaction

  If the energy change = +ve number, then it is ENDOTHERMIC. The reaction absorbs energy from the surroundings.
• Definition of Exothermic Reaction

  If the energy change = -ve number, then it is EXOTHERMIC. The reaction releases energy to the surroundings.
• Calculating Overall Energy Change

  The overall energy change of a reaction is the difference between the energy needed to break bonds in the reactants and the energy released when bonds are formed in the products. This is calculated as: Overall energy change = (energy needed to break bonds) - (energy released when bonds are made).
• Exothermic Reaction Condition


  In an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break existing bonds.
• Endothermic Reaction Condition


  In an endothermic reaction, the energy needed to break existing bonds is greater than the energy released from forming new bonds.
• Basic Design of a Chemical Cell

  A chemical cell typically consists of two different metals separated by a conducting fluid (electrolyte) in a sealed container. This design enables the flow of electric current.
• Metal Electrode Designation


  The more reactive metal forms the cathode (negative electrode), losing electrons to the circuit. Examples: Mg → Mg2+ + 2e-. The less reactive metal forms the anode (positive electrode), gaining electrons from the circuit.
• Simple Cell Design and Batteries

  A simple cell is created by connecting two different metals in contact with an electrolyte. Batteries consist of two or more cells connected in series to provide a greater voltage. Non-rechargeable cells and batteries stop functioning when one reactant is consumed. Alkaline batteries are a type of non-rechargeable battery.
• Hydrogen vs Petrol Advantages

  Hydrogen Advantages:

  • Only produces water as a waste product
  • No pollution
  • No contribution to global warming
  • More efficient in making electricity

  Petrol Advantages:

  • Longer distance between refuelling
  • Wide availability of refuelling stations
  • Petrol cars are generally cheaper
• Hydrogen and Petrol Disadvantages

  Hydrogen Disadvantages:

  • Car's power and speed may be reduced
  • Limited driving range before refuelling
  • Difficult to obtain hydrogen
  • Cars are more expensive

  Petrol Disadvantages:

  • Produces carbon dioxide, contributing to global warming
  • Generates air pollution, including smog and acid rain