Calorimetry
Objective
lesson 6
chapter 9
You will be able to
Define calorimetry qualitatively and quantitatively.
Identify various types of calorimeters.
Calorimeter: a device that measures the heat
absorbed or released during a chemical
reaction.
What is going to happen when the burner is lit?
Experimental Design
Chemical changes involve potential energy, which
cannot be measured directly
Chemical reactions absorb or release energy with the
surroundings, which cause a change in temperature of
the surroundings (and this can be measured)
In a calorimetry experiment, we set up the experiment so
all of the energy from the reaction (the system) is
exchanged with the surroundings
∆Esystem = ∆Esurroundings
In an exothermic reaction, the heat is released
into the water. The amount of heat is measured
as a temperature change in the water and can be
calculated as Qwater = mc∆t
In an endothermic reaction, the heat is absorbed
from the water. The amount of heat is measured
as a decrease in the temperature of the water
and can be calculated as Qwater = mc∆t
Calorimetry Process
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·
·
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Measure the initial temperature of the water.
Add the reactants to the calorimeter and let the reaction proceed.
Stir continuously to evenly distribute the heat.
Record the maximum change in temperature of the water.
Assumptions made:
· The calorimeter is isolated (no heat is lost or gained to the
environment)
· Thermal energy exchanged with the materials of the calorimeter is
negligible
· Dilute solutions have the same heat capacity as water
Example 1
50.0mL of 1.00 mol/L HCl (aq) is added to 50.0mL of 1.00 mol/L
NaOH(aq). The initial temperature is at 23.5˚C. The temperature
rises to 30.1˚C. What is the molar enthalpy of neutralization for
HCl in this reaction?
Example 2
5.00 g of calcium chloride (CaCl2) is dissolved in 100mL of water
in a coffee cup calorimeter.
Calculate the enthalpy change given that the temperature
changed from 23.0˚C to 34.0˚C
Calculate the molar enthalpy of solution for calcium chloride.
Example 3
When 1.00 L of a 1.00 mol/L Ba(NO3)2(aq) solution is mixed
with 1.00 L of a 1.00 mol/L Na2SO4(aq) solution, a white
precipitate forms and the temperature increases from 25.0˚C to
28.1˚C. What is the molar enthalpy of reaction for Ba(NO3)2(aq)?
Assignment
Text p. 355 #7-12
Worksheet assignment #6