C7 Energy Changes

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  • Energy Changes
    • C7.1 Exothermic and Endothermic Reactions
      • Energy is conserved in chemical reactions. It is neither created nor destroyed
      • A reaction in which energy is transferred from reacting substances to their surroundings is called an exothermic reaction
      • A reaction in which energy is transferred to the reacting substances from their surroundings is called an endothermic reaction
    • C7.2 Using Energy Transfer From Reactions
      • Exothermic changes can be used in hand warmers and self-heating cans.
      • Endothermic changes can be used in instant cold packs for sport injuries.
    • C7.3 Reaction Profiles
      • You can show the relative difference in the energy of reactants and products on reaction profiles
      • Bond breaking is endothermic, whereas bond making is exothermic
    • C7.4 Bond Energy Calculations
      • Energy must be supplies to break the bonds between atoms and reactants
      • When new bonds form energy is released
      • In an exothermic reaction, the energy released when new bonds are formed is greater than the energy required to break the bonds
      • In an endothermic reaction, the energy released when new bonds are formed is less than the energy need when bonds are broken
      • You can calculate the overall energy change in a chemical reaction using bond energies
    • C7.5 Chemical Cells & Batteries
      • Metals tend to los electrons and form positive ions
      • When two metals are dipped in a solid solution and joined to a wire, the more reactive metal will donate electrons to the less reactive metal, this forms a simple electrical cell
      • The greater the difference in reactivity the higher the voltage produced
    • C7.6 Fuel Cells
      • Much of the world relies on fossil fuels. However, they are non-renewable and they cause pollution
      • Hydrogen is one alternative fuel. It can be burnt in combustion engines or used in fuel cells to power vehicles
      • Hydrogen gas ix oxidised and provides a source of electrons in the hydrogen fuel cell in which the only waste product is water.

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