U3 S3 L1
Calorimetry
Textbook Readings MHR
•pages 660-661: The Technology of Heat Measurement
•pages 665-667: Using a Calorimeter to Determine the Enthalpy of a Reaction
•pages 673-674: Bomb Calorimetry
Textbook Practice Items MHR
•page 667: items 5, 6 and 7
•page 675: items 8, 9 and 10
•page 676: items 1, 2, *3 and *7
•page 704: item *10
•page 707: items 17, 18 and 21
Upon completion of this lesson, you should be able to:
•
perform calculations based on data collected from simple calorimetry
experiments involving aqueous species to determine the molar heat of
reaction
•
perform calculations based on data collected from bomb calorimetry
experiments to show how energy changes associated with chemical
changes can be used to determine reference data like molar heats of
combustion and heat capacity
•
Calorimetry is the process of determining the
energy change (q) associated with a physical
or chemical change.
qqsys = - qsurr
•
There are two basic types of calorimetry:
1. Simple (constant pressure)
-Surrounding is the water in the calorimeter.
q = mcwater∆T
where Cwater=4.19 J/g•C
2. Bomb (constant volume) calorimetry
-
Surrounding is the calorimeter and its contents
In these case the calorimeter contsnt ( specific heat of the
calorimeter) is known.
q = Ccal∆T
where Ccal = ___kJ/C (ie: no mass)
4 Assumptions of Calorimetry:
1.
The calorimeter is an isolated system, in that neither energy nor matter
is lost or gained to the outside environment.
2.
The first law of thermodynamic holds true. That is, energy is transferred
from the system to the surroundings (vice versa).
3.
Energy absorbed or released by the calorimeter itself is considered
negligible.
4.
Solutions involved in the chemical reactions are consider to be dilute
and thus would have the density and specific heat capacity of pure
water.
1
A volume of 50.0 mL of 0.50 M hydrochloric acid at 22.5°C was mixed with 50.0 mL
of 0.50 M sodium hydroxide solution also at 22.5°C in a simple calorimeter. The
highest temperature reached after mixing was 26.0°C. Calculate the molar heat of
reaction of sodium hydroxide.
2
A 1.23 g sample of ethyne, C2H2, undergoes complete combustion in an oxygen
bomb calorimeter resulting in a temperature increase of 9.50°C. The heat capacity of
the calorimeter is 6.49 kJ/°C. Calculate the molar heat of combustion for ethyne.
4
In order to obtain calibration data for a bomb calorimeter, three 2.50 g samples of
methanol were burned. The average temperature change of 4.23°C was recorded.
The molar heat of combustion of benzene is -726 kJ/mol. Calculate the heat capacity
of the bomb calorimeter