CHEM 120 Lecture Notes - Lecture 4: Gas Thermometer, Intensive And Extensive Properties, Heat Transfer

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7.2 THERMOCHEMISTRY:
Heat (q): Is the quantity of energy q, transferred between the system & its surroundings
(i.e. across a boundary) because of temperature difference
- It is the “energy in transit” and flows from the warmer to the colder body (e.g.
coffee cup gets cooler, the hotter object has exchange)
- Heat flow conduction (pan), radiation, convection (oven, the interfaces can
flow)
- Objects do not contain heat, there is only heat flow when there is a temperature
difference, No Temp Change = No Heat Flow
o Heat is only transitory/temporary
Temperature (T): A measure of the average energy per particle of the microscopic
motions in the system (intensive quantity)
o KE = 3/2 RT/NA gases
- Solids: microscopic motions are vibrations (KE)
- Liquids: more degrees of freedom for motion (e.g. inter/intramolecular vibrations,
translational/rotational motion, etc.)
- Molecules are in constant motion, cooler temp lower amplitude/ high temp
higher amplitude
Heat & Temperature: Heat flows between 2 bodies (A&B) in “thermal contact” until the
average energy (per particle) of the microscopic motions is equal (i.e. until TA=TB)
o Heat transfer by conduction/convection: collisions between atoms at the
surface/boundary result in heat flow (KE transfer pool balls)
Zeroth Law of Thermodynamics: If the two systems (A&B) are separately in thermal
equilibrium with a third system, C (if there is no heat flow between A&C and B&C) then
they are in thermal equilibrium with each other!
o Important because its possible to define Temperature, which is a measure
of the average KE per particle and thermometer (third system C)
E.g. gas thermometer might measure the pressure of a fixed
volume of gas to indirectly determine T (   same P
same T
Heat Capacity (C): the quantity of heat required to change the temperature of a system
by 1 degree (depends on system & material)
- Molar heat capacity (system is one mole of substance)
- Specific heat capacity (c) (system is one gram of substance)
- Heat Capacity (C) (mass x specific heat = mc)
“c” is an intensive quantity which “C” is an extensive quantity;
C depends on the size of the system while c only depends on the nature of the system
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CHEM 120 Full Course Notes
26
CHEM 120 Full Course Notes
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26 documents