Chemistry Chemical Energetics

• Exothermic reactions release energy to their surroundings (negative enthalpy change).
• Endothermic reactions absorb energy from the surroundings (positive enthalpy change).
• Energy Level Diagram

  
• Energy Profile Diagram

  
• Examples of Exothermic Reactions

  Combustion

  Acid-Base neutralisation

  Rusting of Iron

  Respiration

  Condensation

  Freezing
• Examples of Endothermic Reactions

  Thermal Decomposition

  Photosynthesis

  Boiling

  Melting

  Sublimation
• Definition of Activation Energy

  Amount of energy needed for chemical reaction to take place
• Definition of Enthalpy Change

  Amount of heat released or absorbed during a reaction
• Which reaction requires the breaking of bonds?

  Endothermic
• Which reaction requires the forming of bonds?

  Exothermic
• How to find value of Enthalpy Chang if Bond Energy is given

  Eg. Given the at Bond Energy of

  C-H is 413,

  C-C is 360,

  C-O is 464,

  O-H is 346

  O=O is 497,

  C=O is 799