28 terms

# PHYS- Chapter 18

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What is the origin and meaning of the word thermodynamics?
The word thermodynamics stems from Greek words meaning "movement of heat."
Is the study of thermodynamics concerned primarily with microscopic processes or with macroscopic ones?
Thermodynamics is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale. This is done by analyzing the collective motion of their particles using statistics.
How much does the volume of gas at 0C contract for each decrease in temperature of 1 Celsius degree when the pressure is held constant?
For every 1 C decrease in temperature, the volume is reduced by 1/273 .
By how much does the pressure of gas at 0 C decrease for each decrease in temperature of 1 Celsius degree when the volume is held constant?
Any container of fired volume changes by 1/273 of its pressure at 0 C, and as a result the temperature changes by 1 C.
If we assume the gas does not condense to liquid, what volume is approached for a gas at 0C cooled by 273 Celsius degrees?
The volume approaches to zero.
What is the lowest possible temperature on the Celsius scale? On the Kelvin Scale?
The lowest possible temperature on the Celsius scales is -271 C. On the Kelvin scale it is 0K.
What else besides molecular kinetic energy contributes to the internal energy of a substance?
In addition to the molecular kinetic energy, the potential energy of molecules contributes to the internal energy of a substance.
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?
In thermodynamics, the principal concern is the change in internal energy in a substance.
How does the law of the conservation of energy relate to the first law of thermodynamics?
The law of conservation states that if the energy of a system is constant, it does not change. If the energy of the system is completely in the form of heat, then the heat in the system is conserved. This relationship is stated in the First Law of Thermodynamics.
What is the relationship between heat added to a system, change in its internal energy, and external work done by the system?
Heat added to the system equals the internal energy of the system plus 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?
When mechanical work is done on a system, the internal energy of this system increases, so the temperature also increases.
What condition is necessary for a process to be adiabatic?
For a process to be adiabatic, a necessary condition is the thermal insulation of the system form its surroundings. Ie. No heat entering or leaving 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?
If work is done on a system the internal energy increases. If work is done by the system, the internal energy decreases.
How do meteorologists express the first law of thermodynamics?
Meteorologists express the First Law of Thermodynamics in the following form "Air temperature rises as heat is added or as pressure is increased"
What is the adiabatic form of the first law?
It is "Air temperature rises or falls as the pressure increases or decreases.
What generally happens to the temperature of rising air? Of sinking air?
The temperature of rising air decrease while the temperature of sinking air increases.
What is a temperature inversion?
Temperature inversion is the condition in which the upward convection of air cease, often because an upper region of the atmosphere is warmer that the region below it.
Do adiabatic processes apply only to gases?
Adiabatic processes do not apply only to gases. Water in oceans is warmed and cooled adiabatically by changes in pressure.
How does the second law of thermodynamics relate to the direction of heat flow?
According to the Second Law of Thermodynamics, heat always flows from hot objects to cold objects but never from cold objects to hot objects.
What three processes occur in every heat engine?
1. Heat is gained from a reservoir of higher temperature, increasing the internal energy of the engine.
2. Some of this energy is converted into mechanical work.
3. Remaining energy is expelled as heat to a lower temperature reservoir sink.
What exactly is thermal pollution?
When the heat expelled by heat engines is undesirable, thermal pollution occurs.
How does the second law relate to heat engines?
Applied to heat engines the second law of thermodynamics is stated as: 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. The rest is expelled to T_cold
Why is the condensation part of the cycle in a steam turbine so essential?
The condensation part of the cycle in a steam turbine is very essential. This is because the condensation of steam results in a reduction of pressure on the back side of the turbine blades, making the steam turbine more efficient.
Distinguish between high quality energy and low quality energy in terms of organized and disorganized energy. Give an example.
High quality energy is the organized energy. It is concentrated and usable. Low quality energy is the non-usable disorganized energy. Example: Molecules of perfume readily go from the bottle to the air.
How can the second law be stated with regard to high quality and lower quality energy?
"In natural processes, high quality energy tends to transform into lower quality energy order tends toward disorder.
With respect to orderly and disorderly states, what do natural systems tend to do? Cana disorderly state ever transform to an orderly state. In natural systems, orderly states tend to transform into disorderly states. However its inverse is not true without doing external work.
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What is the physicist term for measure of amount if disorder?
Entropy measures the amount of disorder.
Distinguish between the first and second laws of thermodynamics in terms of whether or not exceptions occur.
The first law of thermodynamics is a universal law of nature to which no exceptions have been observed. However, the Second law of thermodynamics may have exceptions if entropy decreases.