energy changes in reactions

• During any reaction there are TWO processes that occur:

  • Bond Breaking
  • Bond Forming
• BOND BREAKING

  where all the bonds in the reactants are BROKEN.

  • This process TAKES IN ENERGY & is ENDOTHERMIC.

  
• BOND FORMING

  The atoms rearrange themselves & new BONDS ARE FORMED to create the products.

  • This process RELEASES ENERGY, making it an EXOTHERMIC process

  
• In an EXOTHERMIC reaction, more ENERGY is RELEASED during BOND FORMING than is TAKEN IN in BOND BREAKING.
• • In an ENDOTHERMIC reaction, more energy is TAKEN IN during BOND BREAKING than is RELEASED during BOND FORMING.
• BOND ENERGIES

  the amount of energy needed to break a specific bond.

  • units: kJ/mol
• energy change = reactants - products = bonds broken - bonds formed
• 432 + 239 - (2 x 427) = -183 kJ/mol

  
• x = 350kJ/mol

  
• -51 = 1841 - (1602 + X)

  • X = 290kJ/mol

  
• 5614 - 6932 = -1318kJ/mol