36 terms

Thermodynamics

Thermodynamics Reading Check and HW
STUDY
PLAY
What is the origin and meaning of the word thermodynamics?
Thermodynamics is from the Greek root meaning movement of heat.
"The study of heat and its transformation into different forms of energy."
Coined by Lord Kelvin
Is the study of thermodynamics concerned primarily with microscopic processes or with macroscopic ones? Why?
Macroscopic, because atoms were unknown at the time thermodynamics was created.
"early workers had only vague notions of atoms, and knew nothing of elections and other microscopic particles; their models invoked macroscopic notions: mechanical work, pressure, temperature."
By how much does the volume of a gas at 0°C contract for each decrease in temperature of 1°C when the pressure is held constant?
the gas will contract 1/273 of its volume for each degree C decrease, given constant pressure.
Suggests that the limit of coldness is -273.15°C-- absolute zero.
By how much does the pressure of a gas at 0°C decrease for each decrease in temperature of 1°C when the volume is held constant?
the gas pressure will decrease 1/273 of its pressure for each °C decrease, given constant volume.
Suggests that the limit of coldness is -273.15°C-- absolute zero.
If we assume the gas does not condense to a liquid, what volume is approached for a gas at 0°C if it is cooled by 273°C?
The gas will contract to a zero volume by this rule. Clearly cannot have a substance with zero volume!
What is the lowest possible temperature on the Celsius scale? On the Kelvin scale?
-273°C
0 Kelvin
*and -459.7°F!
Is the principal concern in the study of thermodynamics the amount of internal energy in a system or the changes in internal energy in a substance? Why?
Thermodynamics concerns changes in internal energy from a substance, because measuring the amount can be complex. Indicated by changes in temperature.
Internal energy is the total E (KE+PE) of submicroscopic particles that make up a substance.
What is the zeroth law of thermodynamics?
Two systems in thermal equilibrium with a third system are in equilibrium with each other.
So named after 1, 2, 3rd laws named.
How does the law of the conservation of energy relate to the first law of thermodynamics?
Adding heat flow to the law of conservation of energy gives the first law of thermodynamics.
"When heat flows to or from a system, the system gains or loses an amount of energy equal to the amount of heat transferred."
Heat added to a system = increase in internal energy + external work done by the system.
What is meant by a system?
a well-defined group of atoms or objects,
molecules, particles.
ex.) body of a living creature, steam in a steam engine, Earth's atmosphere
What is the relationship among heat added to a system, a change in the system's internal energy, and external work done by the system?
The heat added to a system is equal to the change in internal energy plus the external work done by the system.
What happens to the internal energy of a system when mechanical work is done on it? What happens to its temperature?
mechanical work done on a system:
internal energy increases
temperature increases
What condition is necessary for a process to be adiabatic?
No heat enters or leaves the system. "impassable"
thermally insulate the system
If work is done on a system, does the internal energy of the system increase or decrease? If work is done by a system, does the internal energy of the system increase or decrease?
work on system: internal energy increase. Bike pump use warms up.
work by system: internal energy decreases. Open tire escaping air cools down valve.
How do meteorologists express the first law of thermodynamics?
Air temperature rises as heat is added or as pressure is increased.
Air temperature may be changed by +/- heat, changing pressure of air (involves work), both.
Solar radiation (heat)
moisture condensation
warm ground contact
What is the adiabatic form of the first law of thermodynamics?
Air temperature rises (or falls) as pressure increases (or decreases).
Characteristic by parts of air (parcels) pressure lessens, allowed to expand and cool. Reduced pressure = reduced temperature.
What generally happens to the temperature of rising air? Of sinking air?
Rising air cools.
Sinking air warms up.
Decreasing and Increasing T
What is a temperature inversion?
When higher elevations in the atmosphere are warmer than lower elevations.
Usually higher elevations are cooler than lower elevations.
*mountains vs valley weather!
Do adiabatic processes apply only to gases? Defend your answer.
Adiabatic processes can even occur in the liquid ocean (deep currents circulating per 1000 years) and inside Earth (convection currents in molten material under crust)
How does the second law of thermodynamics relate to the direction of heat flow?
Heat of itself never flows from a cold object to a hot object.
In winter, heat flows from warm inner house to cold outer air. In summer, heat flows from hot exterior to cooler interior.
Heat flow = from hot to cold
What three processes occur in every heat engine?
Heat flows into a system from a hot reservoir, work is done by the system, and heat flows out to a cold reservoir
What exactly is thermal pollution?
Undesirable discarded heat
*expelled heat from oven on a hot summer day= undesirable
*expelled heat from laundry on a cold winter day= desirable
How does the second law of thermodynamics relate to heat engines?
The second law expresses the maximum efficiency of a heat engine in terms of hot and cold temperatures.
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, while the rest is expelled at TTn 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, while the rest is expelled at TTn 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, while the rest is expelled at *T*(cold).
"All systems tend to become more and more disordered as time goes by."
Why is the condensation part of the cycle in a steam turbine so essential?
To prevent the backward push on the turbine blades by exhaust gasses
Without condensation (pressure), counterproductive
Distinguish between high-quality energy and low-quality energy in terms of organized and disorganized energy. Give an example of each.
High-quality energy is organized.
ex.) gasoline, turbulent water
Low-quality energy is disorganized.
ex.)dispersed thermal energy, water pooled after waterfall
How can the second law of thermodynamics be stated with regard to high-quality and lower-quality energy?
High-quality energy tends to transform into lower-quality energy.
Order tends toward disorder.
Quality of energy is lowered with each transformation, as energy degrades
With respect to orderly and disorderly states, what do natural systems tend to do? Can a disorderly state ever transform into an orderly state? Explain.
Natural systems tend to go from order to disorder unless work is done on them to bring order out of disorder.
*Open lid of bottle; molecules escape and disorder; will not order back into bottle!
What is the physicist's term for the measure of the amount of disorder?
Entropy: natural dispersing or degrading of energy.
ex.) Energy locked in chem bonds in wood degrades when wood burns.
Total amount of entropy in a system tends to increase with time (while available energy for work decreases)
*batteries go dead even w/o use
Discuss the first and second laws of thermodynamics in terms of whether or not exceptions occur.
1st law has no exceptions. 2nd law exceptions are possible but improbable. Law nutshell:
"You can't win" (can't get more output than input)
"You can't break even" (can't get as much output as input)
"You can't get out of the game" (entropy forever increases)
What is the third law of thermodynamics?
No system can have its absolute temperature reduced to zero.
When air is quickly compressed, why does its temperature increase?
The pressure is increased, thus air temperature increases as per the 1st Law and meteorology:
Air temperature rises as heat is added or as pressure is increased.
What is the ultimate source of energy in coal, oil, and wood? Why do we call energy from wood renewable but energy from coal and oil nonrenewable?
Sunlight is the ultimate source of energy in coal, oil and wood. However, the energy in wood is renewable relatively quickly by new growth, while coal and oil's energy is from the Sun of many years ago.
How does the ideal efficiency of an automobile relate to the temperature of the engine and the temperature of the environment in which it operates? Be specific.
Ideal efficiency proves an upper limit to all heat engines. Friction is always present in all engines, and efficiency is always less than ideal. Only some of the heat can be converted to work, even if the environment conditions are ideal. Heat is expelled to the environment via the cooling system and exhaust.
Could you cool a kitchen by leaving the refrigerator door open and closing the kitchen door and windows? Explain.
The heat flow will be from the warmer kitchen air to the cooler refrigerator.
A refrigerator moves heat from cold to warm. Why does this not violate the second law of thermodynamics?
The refrigerator uses a pump to move a fluid around, compress and evaporate the fluid, causing it to absorb and release heat. The cooling of the interior of a refrigerator does not violate the laws of thermodynamics because work has to be input to the system in order to run the compressor that helps pump the heat out of the refrigerator.In each instance where there is heat transfer, the heat moves from the warmer to the colder part of the system - in keeping with the second law.
Also, the 2nd Law can have exceptions.
The ocean possesses enormous numbers of molecules, all with kinetic energy. Can this energy be extracted and used as a power source? Defend your answer.
...
YOU MIGHT ALSO LIKE...