CHMA10H3 Lecture Notes - Lecture 6: Calorimetry, Calorimeter, Exothermic Process

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CHMA10 Lecture 6: Measuring Internal Energy Changes and Enthalpy
- 6.5: Measuring Changes in Internal Energy for Chemical Reactions
o Any change in the internal energy of a system must include 2 components: heat
(q) and work (w)
o Bomb Calorimetry: utilized to create constant volume situations
Very helpful for finding the internal energy of a reaction
Bomb Calorimeter: piece of equipment designed to measure changes in
internal energy for combustion reactions
In these devices, the reaction occurs in a sealed container called a
bomb
o This ensured that the reaction occurs at a constant volume
Process of using a bomb calorimeter
o 1: Put the sample of known mass that is to be burned into
a cup with an ignition wire
o 2: Seal the cup into the bomb which is willed with oxygen
gas
o 3: Place the bomb into a water filled, insulated container
equipped with a stirrer and thermometer
o 4: Ignite the sample with a wire coil and monitor the
temperature
The temperature change is related to the heat
absorbed by the entire calorimeter assembly
Remember the equation for finding the change in internal energy of a
reaction
Ur = q + w
= q + P V
In a constant volume situation, P V always equals 0
This means work is equal to 0
Substances in the system may be expanding but no work is
actually being done
o There is no displacement cost needed to create a change
in volume
Therefore we can use the following equation to solve for the heat gained
or lost by the calorimeter
qcalorimeter = Ccalorimeter T
o Ccalorimter: Heat capacity of the calorimeter
o T : change in temperature
Key equations
o Heat absorbed by the calorimeter = heat released by the
reaction
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