Energy Changes

• What is the conservation of energy principle?

  Energy is observed in chemical reactions. The amount of energy in the universe at the end of a chemical reaction is the same as before the chemical reaction takes place.
• What is an exothermic reaction?

  When energy is transferred to the surroundings and the surrounding's temperature increases.
• Give examples of exothermic reactions

  Oxidation

  Neutralisation

  Combustion
• What is an endothermic reaction?

  When energy is taken in from the surroundings so the surroundings temperature decreases
• What are examples of Endothermic reactions

  Self Heating Cans

  Sport Injuries Packs

  Thermal Decomposition

  Reaction of citric acid and sodium hydrogencarbonate
• What is activation energy?

  The minimum amount of energy needed for the particles to react
• What is a reaction profile?

  The reaction profile is a graph which shows the relative energy of reactants and products, as well as the activation energy.
• Draw an endothermic and exothermic reaction profile

  Exothermic reaction - The energy of reactants should be higher than the products

  Endo - Opposite way

  
• What occurs in a chemical reaction in terms of bond energies? Describe exothermic and endothermic reactions in terms of bonds breaking/forming.

  Energy is supplied to break bonds and energy is released when bonds are made

  Exothermic - Energy released from making the bonds is greater than the needed to break the bonds

  Endothermic - Energy released from making the bonds is less than the needed to break the bonds
• What is the equation to find the enthalpy change in terms of bond changes?

  The energy of reaction = sum of bonds broken - sum of bonds made
• What is a cell?

  A cell is composed of two electrodes dipped in an electrolyte solution. It produces electricity from a chemical reaction.
• What is a battery?

  A battery consists of two or more cells connected in a series.

  
• State the advantages and disadvantages of using cells and batteries.

  (+) cheap, some are rechargeable, a convenient source of electrical energy

  (-) harmful chemicals