Calorimetry

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Calorimetry
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Calculating Heat

• Q can be found experimentally by measuring the
  heat flow accompanying a reaction
• This is done by measuring temperature
• This process is called calorimetry

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Specific Heat (c)

• This is amount of heat required to raise the
  temperature of 1g of a substance 1ºC
• Specific heat is different for different
  substances
• A lower specific heat means that it takes a small
  amount of heat to change the substances
  temperature

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Calculating the Heat Transfer

• Heat transfer can be calculated using
  Q (c)(m)(?t)
• The specific heat of iron(III) oxide is
  .75 J/g ºC. What is the heat required to
  increase the temperature of a 1.75 g sample from
  25ºC to 380ºC?

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Enthalpy (?H)

• ?H is Q at a constant pressure
• ?H is always the J given off per mole of reactant
  (J/mol)

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Example

• When 50 ml of a 1.0 M HCl and 50 ml of a 1.0 M
  NaOH solution are mixed, the temp in a
  calorimeter increases from 21.0 ºC to 27.5ºC. The
  total volume of the end solution is 100 ml, its
  density is 1.0 g/ml, and its specific heat is
  4.18 J/gºC. Find the enthalpy change (heat of
  reaction)?

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Water Chamber Calorimetry

• Heat lost by a reaction is gained by a quantity
  of water in a calorimeter
• Heat lost Heat gained
• C(water) 4.184 J/gºC

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Example

• In a calorimeter containing 100 g of water at
  21ºC, a reaction is carried out in which 3.5 g of
  NH4NO3 decomposes into N2O and H2O. The
  temperature raises to 25ºC. Find the heat of
  reaction.