Unit 4 Flashcards
(25 cards)
Kinetic theory of gases
-gas consists of a large number of identical molecules separated by distances that are great compared to their size
-gas molecules are constantly moving in random directions with a distribution of speeds
-molecules can collide elastically with each other (bounce off each other with no loss of kinetic energy) but exert no forces on one another between collisions
-the collisions of molecules with the walls of the container are also elastic (no loss of KE during collision
Maxwell-Boltzmann distribution
-f(v) = 4Π ( m / 2ΠKbT )^3/2 v^2 e ^ [(-mv^2) / (2KbT)]
-area under graph (f(v)) describes the fraction of molecules that have speeds between v1 and v2 (all equal to 1)
-mp = most probable speed
-<v> = average speed</v>
How temperature and mass effect MB distribution
- low temperature = higher/slimmer peak, slower average speed
- high temperature = smaller/wider peak, faster average speed
- larger mass = higher/slimmer peak, slower average speed
- smaller mass = smaller/wider peak, faster average speed
mean (average) speed MB graph
<v> = √ [(8KbT) / (ΠM)]
<v> = 1.128 (vmp)
-lies farther right on graph than most probable (vmp)
</v></v>
most probable speed (vmp)
vmp = √ (2KbT / M)
Boltzmann constant, Kb
-constant used to relate the average kinetic energy of particles in a gas to the temperature of that gas
-Kb = R / Na
KE (translational) total
-3/2nRT (for monatomic gases)
-change in KE is directly proportional to change in temperature
Thermodynamics
study of the interconversion, transfer, and dispersal of energy among its various forms
work (w)
-the product the external force F acting on a body and its displacement d
-transfer of energy through mechanical process
heat (q)
- a means by which, without mechanical interaction, energy is transferred from a hot body to a colder body when the two are placed in thermal contact with one another
-transfer of energy due to difference in temperature
Joule to calorie
4.184 J = 1 calorie
system
-any part of the universe that we want to focus attention on
surroundings
-part of the universe with which the system can exchange energy or matter
first law of thermodynamics
-in any process, energy can be changed from one form to another (eg potential to KE) and energy can be transferred from one object to another (as heat or work), but energy is never created or destroyed
-(law of conservation of energy)
isolated system
-one that does not exchange energy or matter
-therefore has no surroundings
closed system
-one that has boundaries that permit energy but not matter to flow in and out
open system
-can exchange both energy and matter with its surroundings
Pressure Volume work
-results when a system is compressed or expanded under the influence of an outside pressure
-Δq > 0, heat is added to system
-Δq < 0, heat leaves the system
-Δw > 0, work is done by surroundings on system
-Δw < 0, work is done by system on surroundings
Pext
-pressure from gas on the outer side of the piston
-w = -Pext (vf - vi)
Internal energy, U
-the sum of the kinetic and potential energies of all the atoms/molecules in the system and can be changed by the flow of heat, work, or both
-ΔU = q + w
-for ideal monatomic gases, U = KE (3/2nEΔT)
-directly proportional to temprature
isothermal
-having or relating to a uniform temperature, or a process that happens at a constant temperature
-ΔT = 0, therefore ΔU = 0
work for reversible gas expansion (wrev)
-wrev= -nRT(V2 / V1)
-more work and heat is transferred by reversible expansion than constant pressure
Adiabatic expansion
-expansion in which heat does not enter or leave the system concerned
-q=0
-ΔU = w
state function
-a property that depends only on the initial and final states of the system, independent of the path taken to get from one to the other
-ΔU ΔV ΔT
