Calorimetry

• Define specific heat capacity

  The amount of energy needed to make 1g of a substance 1 degree(1K) hotter (Jg-1K-1)
• What equation finds the amount of heat energy given out?

  q=mc∆T
• What equation finds enthalpy change per mole?

  Enthalpy change = 2 / number of moles reacting
• What are calorimetry techniques designed for?

  To reduce heat loss
• What is one way to reduce heat loss errors in calorimeters?

  By measuring the heat capacity of the calorimeter
• Describe how to find the heat capacity of reactions taking place in solutions

  -The reaction is carried out in an insulated beaker and the temperature change is measured

  -The reaction must be fast so the max. temperature is reached quickly

  -The specific heat capacity of the solution must be taken as its value and we usually use the mass of water in the calculation
• Describe how to find heat capacity in flame calorimeters

  -Flame calorimeters are used to find the enthalpy of combustion

  -The fuel, which is in a bottle with a wick, is burned so that the heat is passed to water which it heats

  -Sometimes the SHC of water is used

  -But, in more accurate flame calorimeters, the actual SHC can be determined by finding the temperature rise when a known amount of substance with an accurately known enthalpy of combustion is tested
• Describe how to find heat capacity is found in bomb calorimeters


  -The most accurate type of calorimeter

  -A known mass of fuel is placed inside a steel container and it is filled with oxygen under pressure

  -The fuel is electrically ignited and heat evolved used to heat surrounding water

  -The heat capacity is found by burning a substance with accurately known enthalpy of combustion
• How is enthalpy of a reaction calculated?

  ∆H - enthalpy of bonds broken - enthalpy of bonds made