CHMA10H3 Lecture Notes - Lecture 5: Thermal Energy, Jmol, Ideal Gas Law

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CHMA10 Lecture 5: Quantifying Heat and Work
- 6.4: Quantifying Heat and Work
o Heat (q): The transfer of thermal energy due to a temperature difference
between the system and surroundings
Thermal energy will always flow from hot to cold
Thermal Equilibrium: the heat transfer between a system and its
surroundings will stop when both reach the same temperature
Temperature (T): measure of thermal energy
Heat Capacity ( c ): amount of heat needed to raise the temperature of a
substance by 1 degree Celsius
Specific Heat Capacity: the amount of heat needed to raise the
temperature of 1 g of a substance by 1 degree Celsius
Molar Heat Capacity: the amount of heat needed to raise the
temperature of 1 mol of a substance by a degree Celsius
Can use all of this information to create a formula to determine heat
when given mass, heat capacity and the change in temperature of a
substance
q = mc T
o Work: can be expressed as a force acting against an external power to carry
something through a distance
We tend to focus mostly on pressure-volume work
Eg: In chemical reactions that release heat, some of the energy released
can do work
The air expanding in the system has the ability to push against an
external force
In this case the external force is the atmospheric pressure
The air pushes against the atmospheric pressure which enables
the displacement of any of the objects nearby
o As a result, a change in volume may occur
W = -F d
The negative in the equation shows that work is being done by
the system on the surroundings
o When heat is released by a system, it will have negative magnitude
Heat flowing into a system will have positive magnitude
o Work done on a system by the surroundings will have a positive magnitude
Work done on the surroundings by a system will have negative
magnitude
o Key Equations
Pressure (P) = Force (F) / Area (A)
Therefore F = PA
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