Chapter 18: Thermodynamics Flashcards
The science of thermodynamics was developed in
The early 19th century
Early thermodynamics invoked macroscopic ideas such as
Mechanical work, pressure, and temperature
The foundation stones of thermodynamics are
1) The conservation of energy
2) The fact that heat flows spontaneously from hot to cold and not the other way around
Absolute zero
There is no upper limit to temperature
Absolute zero was the molecules have
Lost all available KE
When the temperature of a gas change, the volume of the gas also
Changes
At zero degrees with pressure constant volume changes by
1/273 for each degree Celcius
Absolute temperature scale is
Kelvin Scale
No negative number on
Kelvin Scale
Absolute zero was
0 K
First Law: When heat flows to or from a system, the system gains or loses an amount of energy equal to
The amount of heat transferred
System:
Group of atoms, molecules, particles, or objects
Three types of systems
1) Open system
2) Closed system
3) Isolated system
1) Open system
System can exchange both matter and energy with surroundings
2) Closed system
System which can exchange only energy with surroundings
3) Isolated system
System in which neither energy nor matter can be exchanged with surroundings
If we add heat, Q, to a sytem, two things can happen:
1) It increases the internal energy, U, of the system (if it remains in the system)
2) It does work on things external to the system (if it leaves the systems)
Heat added equal to
Increase in internal energy plus with external work done by the system
Q equal to (theta U) plus with
W
First Law of Thermodynamic is a restatement of
The law of conservation of energy
Energy can neither be
Created nor destroyed
Positive heat in, the positive work
Out of the convention
When work is done on a system, for example, compressing air in a tire pump, the temperature of the system
Increases
Adiabatic processes
One of the thermodynamic processes which occur without any heat transfer between the system and the surroundings
Heat added to system equal to
0
Increase/Decrease in internal energy equal to
Work done on/by system
Compressing or expanding a gas while no heat enters or leaves the system is an
Adiabatic process
Adiabatic conditions are achieved by
Thermally insulating a system from its surrounding or performing the process so rapidly that heat has no time to enter or leave
Blow air on your hand first with your mouth wide open, then with puckered lips. In which case is the air coming out of your mouth cooler?
When your lips are puckered
Thermodynamics is useful to meteorologists when
Analyzing weather
1st Law: Air temperature rises as heat is added or as pressure is increased
1) Radiation back from Earth
2) Moisture condensation (warming process)
3) Contact with ground
In the adiabatic form (no heat is added), the first law becomes
Air temperature rises (or falls) as pressure increases (or decreases)
Adiabatic processes in the atmosphere occur in large parts of the air, called
Parcels
Parcels are large enough that outside air does not appreciably mix with the
Air inside them
As parcels of air rise, they experience
Lower pressure so they expand
Expanding air cools down to
10 degrees Celsius for every 1 km rise in altitude
Air continues to rise and expand as long as it has a
Higher temperature than its surrounding
When it gets cooler than the surroundings, it sinks
No heat is added or taken away
As parcels of air drop, they experience
Higher pressure and heat up
Parcels expand and cool with
Lower pressure
Parcel compress and warm with
Higher pressure
If cooler air occurs at an altitude lower than warmer air
Temperature Inversion
During a temperature inversion, if rising warm air is
Denser than upper layers of warm air, it will no longer rise
Second laws of thermodynamics:
Heat always flows from hotter to cooler objects
Heat can flow hot only when
On the system energy from another source
A heat engine is
Any device that converts internal energy into mechanical work
Basic ideas of thermodynamics:
Mechanical work can be obtained only when heat flows from a higher temperature to a lower temperature
Only some of the heat can be transferred into
Work done
Every heat engine has
1) A reservoir of heat at a high temperature
2) A sink at lower temperature
Every heat engine
1) Gather heat from the reservoir at high temperature
2) Converts some of this heat into mechanical work
3) Expels the rest of the heat to the sink at lower temperature
When work is done by a heat engine operating between two temperatures, T(hot) and T(cold) only some of the input heat at T(hot) can be converted to
Work and the rest is expelled at T(cold)
The ideal (maximum possible) efficiency of a heat engine was determined by
Carnot
In real heat engine, the efficiency is actually
Less than ideal, due to friction
Restatement of the 2nd law:In natural processes, high quality energy tends to
Transform into lower quality energy order tends to disorder
Processes in nature moving from disorder to order do not occur without
External assistance
Entropy
Measure of the amount of disorder in a system
If disorder increases, then entropy is
Increase
Entropy can decrease if work is
Put into the system
Living organism take in food or extract energy from
Their surrounding and become more organized
This energy is then used for various processes that help
Maintain the organism’s internal order and decrease entropy
Net entropy in the universe is
Continually increasing
We say net because there are some regions in which energy is
Being organized and concentrated
The second law of thermodynamics is
A probabilistic statement
Given enough time, even the most improbable states may occurs, entropy may
Sometimes decrease
The perpetual motion of air molecules could momentarily become
Harmonious in a corner of the room and these situations are possible but they are not probable
