(NR) Feb 8, 2011 : ENERGY AND PERCENT YIELD

• Enthalpy is the energy stored in chemical bonds
• Symbol of Enthalpy is H
  - units of Joules (J)
• Change in Enthalpy is delta H
• In Exothermic reactions enthalpy decreases
• In Endothermic reactions enthalpy increases
  
       CALORIMETRY
  • To experimentally determine the heat released we need to know THREE things:
    
    1. TEMPERATURE CHANGE (delta T)
    2. Mass (m)
    3. Specific heat capacity (C)
       Cw= 4.19 J/g degrees C
     These are related bythe equation:
          delta H = mCdeltaT            
                     = mC(Tf-Ti)
    
    
    PERCENT YIELD
    
    • The theoretical yield of a reaction is the amount of products that SHOULD be formed.
    • The  actual amount depends on the experiment
    • The percent yield is like a measure of success.
      - How close is the actual amount to the predicted amount?
      
      
      %YIELD = [ACTUAL/THEORETICAL] x 100