thermodynamics

Created by

Leah beyram

Cards (43)

the change in internal energy of an object is...
directly proportional to the change in temperature
what happens when a gas expands  
work is done on its surroundings by exerting pressure on the walls, volume increases
what happens when a gas compresses  
work is done in the gas (-W), volume decreases (-V)
how can work done be calculated on a p-V diagram
the area under the diagram
what is the first law of thermodynamics
energy supplied by heating = change in internal energy + work done on the system
what does a positive value for internal energy mean  
internal energy increases(+U), heat is added to the system(+Q), work is done on the system (-W)
what does a negative value for internal energy mean  
internal energy decreases (-U), heat is taken away (-Q), work is done by the system (+W)
how is constant pressure represented on a p-V graph
straight line
what is entropy  
a measure of how disordered a system is
when can entropy increase  
increase in temperature so particles vibrate more making them able to freely move

when a solid dissolves in a solvent

when a gas diffuses in a container
when can entropy decrease  
decrease in temperature, particles become less able to move as they become more ordered
what is a reversible process  
when there is no overall change in entropy as the system and its surroundings are returned to their original state
what is an irreversible process
when there is an increase in entropy as the system and its surroundings cannot return to their original states
processes in real isolated systems are almost always...
irreversible and the entropy always increases
what is an isolated system
a system in which neither matter nor energy can be transferred in or out
the entropy of a non-isolated system can... 
decrease locally but is compensated by an equal or greater increase in the entropy of the surroundings
how do you calculate entropy
S = Q / T
how can entropy on a microscopic level be calculated  
S = kB x ln(number of possible microstates of the system)
what are microstates  
the number of states or possible arrangements of the particles in the system
what is a state  
any microscopic or macroscopic property that is known about the system
when particles are confined to one compartment... 
we know the location of all the particles, therefore the number of microstates in the initial volume is 1
what happens when the partition is removed  
particles can spread out and occupy either one of the two compartments
what is the change in entropy equation
S = kB x ln(2^N)
what happens as to the space a gas occupies as it expands  
it doubles and gains an amount of entropy
what is the second law of thermodynamics  
in every process, the total entropy of an isolated system always increases
what is clasius's form of the second law of thermodynamics  
thermal energy cannot spontaneously transfer from a region of lower temperature to a region of higher temperature
what is kelvin's form of the second law of thermodynamics  
when extracting energy from a heat reservoir, it is impossible to convert it all into work
what is an isobaric process
a process in which no change in pressure occurs
what is an isovolumetric process
where no change in volume occurs and the system does no work
what is an isothermal process
where no change in temperature occurs
what is an adiabatic process  
where no heat is transferred into or out of the system
how can an adiabatic process modelled  
pV^5/3 = constant
what does a heat engine do
converts thermal energy into mechanical work
what is a closed cycle  
one in which the system returns to its initial state
what are the steps in the operation of a cyclic heat engine process 
1 - extract heat from a hot reservoir
2 - use some of the extracted heat to perform work
3 - release excess heat into a cold reservoir
4 - repeat cycle
what is the net work done by the engine
W(out) = heat transferred from hot reservoir to engine - heat transferred from engine to cold reservoir
what are the stages of the carnot cycle  
1 - isothermal expansion
2 - adiabatic expansion
3 - isothermal compression
4 - adiabatic compression
what happens during an isothermal expansion  
the gas absorbs heat from a hot reservoir at a temperature
work is done by the gas as it expands
work done by the gas = heat gained
what happens during adiabatic expansion  
gas continues to expand
gas does work on the surroundings as its volume increases and pressure decreases
gas cools down from TH to TC but no thermal energy is transferred
what happens during isothermal compression  
gas is compressed and transfers heat to a cold reservoir at TC
work is done on the gas as it is compressed, volume decreases, temperature is constant
work is done on the gas = heat is lost