Calorimetry

1
Calorimetry

• Learning Target
• What is calorimetry?
• How does a calorimeter work?

2
What is Calorimetry?

• Calorimetry study of heat flow and heat
  measurement.
• Calorimetry experiments determines the heat/
  enthalpy changes of reactions by making accurate
  measurements of temperature changes in a
  calorimeter.

3
Heat capacity Specific Heat

• Calorie The amount of heat or energy needed to
  raise the temperature of 1g of water by 1 C
• Heat capacity the amount of heat needed to
  raise the temperature of the object by 1C.
  (depends on mass and composition of the object).
• Specific heat (C) Heat capacity of 1g of a
  substance. Units J/(gxC)
• Specific heat of water C 4.184 J/(gxC)
• 1 calorie 4.184 J

4
Example

• Find the specific heat of a 32.2g sample of
  Nickel if the temperature is increased by 3.5 C
  when 50. J of energy is added?
• To solve Place the given values in the unit of
  specific heat.
• CNi ____50.J______
• (32.2g x 3.5 C)
• CNi 0.44 J/(gxC)

5
Heat Temperature

• Transfer of heat can be measured by change in
  temp.
• A small change in temperature does not always
  mean that a small quantity of heat was
  transferred. A small change in temperature can
  be produced by a large quantity of heat in an
  object with high heat capacity.

6
Calorimeter

• A calorimeter is a well-insulated cup filled with
  a certain mass of water in which a reaction is
  carried out.

7
Calorimeter

• The temperature of the water is taken before the
  reaction takes place, and it is recorded as the
  initial temperature Ti.
• The final temperature of water is recorded at Tf.
• Heat changes in the calorimeter are denoted as q.

8
Calorimeter

• Since the reaction takes place in water, water
  acts as the surrounding.
• Heat changes in the water are called qsurr while
  heat changes in the reaction are called qrxn.
• The heat transferred between the reaction and the
  surrounding are opposite processes.
• Therefore qrxn -qsurr

9
Calorimeter

• The amount of heat absorbed/ released in water is
  determined using the mass of water m, specific
  heat of water C, and change in water temperature.
• qsurr m x C x (Tf Ti)

10
Example!!

• When 4.25g of NH4NO3 is dissolved in 60.0g of
  water, the temperature drops from 21C to 16.9C.
  Find the ?H for the solution process.