Calorimetry
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
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 substance’s
temperature
Calculating the Heat Transfer
 Heat transfer can be calculated using
Q = (c)(m)(Δt)
 The specific heat of iron(III) oxide is 0.75 J/g ºC.
What is the heat required to increase the
temperature of a 1.75 g sample from 25ºC to 380ºC?
Enthalpy (ΔH)
 ΔH is Q at a constant pressure
 ΔH is always the J given off per mole of reactant
(J/mol)
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)?
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
Example
 30.0 g of water at 1000C is mixed with 50.0g of water
at 150C and allowed to come to thermal equilibrium.
What is the final temperature of the mixture?
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.