thermodynamics Flashcards
thermodynamics
the study of the flow of energy in the universe
zeroth law of thermodynamics
based on a simple observation: when one object is in thermal equilibrium with another object, and the second object is in thermal equilibrium with a third object, then the first and third object are also in thermal equilibrium. no net flow of heat occurs
temperature
is a physical property of matter related to the average kinetic energy of the particles. Differences in temperature determine the direction of heat transfer
heat
the transfer of thermal energy from a hotter object with higher temperature (energy) to a colder object with lower temperature (energy). cannot spontaneously transfer energy from a cooler object to a warmer one without work being done on the system.
Unit is Joule (J)
Fahrenheit
absolute zero= -460 freezing point of water= 32 boiling point of water= 212
Celsius
absolute zero= -273 freezing point of water= 0 boiling point of water= 100
Kelvin
absolute zero= 0 freezing point of water= 273 boiling point of water= 373
absolute zero
theoretical temperature at which there is no thermal energy
Celsius to Fahrenheit
F= 9/5C+32
Celsius to Kelvin
K=C+273
thermal expansion
an increase in the length or volume of a substance as a result of an increase in temperature
thermal expansion equation
deltaL = alpha x L x deltaT
deltaL=change in length
alpha= coefficient of linear expansion
L= orignial length
volumetric thermal expansion
deltaV = beta x V x delta T
beta= coefficient of volumetric expansion
coefficient of linear and volumetric expansion
beta = 3alpha
system
the portion of the universe that we are interested in observing or manipulating
isolated systems
are not capable of exchanging energy or matter with their surroundings. total change in internal energy must be zero
closed system
are capable of exchanging energy, but not matter, with its surroundings
open systems
can exchange both matter and energy with the surroundings
ex: boiling water, humans
state functions
thermodynamic properties that are a function of only the current equilibrium state, think vectors and scalars
include pressure, density, temp, volume, enthalpy, internal energy, gibbs free energy, and entropy
process functions
describe the path taken to get to from one state to another, think vectors and scalars
include work and heat
first law of thermodynamics
states that the change in the total internal energy of a system is equal to the amount of energy transferred in the form of heat to the system, minus the amount of energy transferred from the system in the form of work
deltaU=Q-W
U=internal energy
Q=energy transferred into the system as heat
W= work done by the system
delta U
negative sign= decrease in temp
postive sign= increase in temp
Heat (Q) in the first law
positive value= heat flows into the system
negative value= heat flows out of the system
Work (W) in the first law
positive value= work is done by the system (expansion)
negative value= work is done on the system (compression)
what are the only two processes that energy can be transferred?
heat and work
little calorie (c not C)
1 c = the amount of heat required to raise 1 g of water 1 degress Celsius.
big calorie (C no c)
1 C = the amount of heat required to raise 1 kg of water 1 degree Celsius
equal to 1000 c
conduction
the direct transfer of energy from molecule to molecule through molecular collisions; must be direct physical contact
convection
the transfer of heat by the physical motion of a fluid over a material. only include gases and liquids
radiation
the transfer of energy by electromagnetic waves, only form of heat transfer that can transfer energy through a vacuum
specific heat (c)
defined as the amount of heat energy required to raise one gram of a substance by one degree Celsius or one unit Kelvin
changes according to its phase
specific heat of water
1 cal/(g K)
heat gained or lost (with temp change)
q=mcAT
AT=delta T
c=specific heat
m= mass
Heat of transformation
during a phase change, heat energy causes energy changes in particles potential energy and energy distribution (entropy), but not kinetic energy. Therefore, phase changes have no change in temperature (kinetic energy), just in the thermal energy
heat gained or lost (phase change)
q= mL
q= amount of heat gained or lost from the material
m= mass
L= heat of transformation or latent heat
heat of fusion
melting point
phase change from liquid to solid (solidification) or solid to liquid (fusion)
heat of vaporization
boiling point
phase change from liquid to gas (evaporation, vaporization) or gas to liquid (condensation)
thermodynamic processes
isothermal, adiabatic, isovolumetric, and isobaric
in each case, some physical property is held constant during the process
isothermal
constant temperature, so no chane in the internal energy
(delta U=0) Q=W
adiabatic
no heat exchange
(Q=0) deltaU= -W
isovolumetric (isochoric)
no change in volume, and therefore no work accomplished
(W=0) deltaU=Q
Isobaric
processes at constant pressure
no special from ofthe first law
Second Law of Thermodynamics
states that objects in thermal contact and not in thermal equilibrium will exchange heat energy such that the object with a higher temp will give off heat energy to the object with a lower temp until the objects have the same temp at thermal equilibrium.
Energy spontaneously disperses form being localized to becoming spread out if it is not hindered from doing so.
entropy (S; J/[molxK])
the measure of the spontaneous dispersal of energy at a specific temperature: how much energy is spread out, or how widely spread out energy becomes in a process
deltaS= Qrev/T
Qrev =the heat that is gained or lost in a reversable process
T= temp in kelvin
changes in entropy with changes in energy
energy distributed into a system, entropy increases
energy distributed out of a system, entropy decreases
