physics chap 12 quiz (key terms, concepts, q&a)
12.3: Second Law of Thermodynamics: Entropy
-Entropy is a measure of a system's disorder: the greater the disorder, the larger the entropy. -Entropy is also the reduced availability of energy to do work. -The second law of thermodynamics states that, for any spontaneous process, the total entropy of a system either increases or remains constant; it never decreases. -Heat transfers energy spontaneously from higher- to lower-temperature bodies, but never spontaneously in the reverse direction.
4. Why does thermal expansion occur?
An increase in temperature causes intermolecular distances to increase.
16. What are two reasonable outcomes of adding heat energy to an inflated balloon?
Constant pressure and increased volume.
40. Why does entropy increase during a spontaneous process?
Entropy increases because energy always transfers spontaneously from a concentrated state to a dispersed state.
73. Two distinct systems have the same amount of stored internal energy. Five hundred joules are added by heat to the first system, and 300 J are added by heat to the second system. What will be the change in internal energy of the first system if it does 200 J of work? How much work will the second system have to do in order to have the same internal energy?
Q first=500 W first= 200 ΔU=500-200= 300J = 300 J; 0 J
15. When an inflated balloon experiences a decrease in size, the air pressure inside the balloon remains nearly constant. If there is no transfer of energy by heat to or from the balloon, what physical change takes place in the balloon?
The average kinetic energy of the gas particles decreases, so the balloon becomes colder.
3. To which mathematical property is the zeroth law of thermodynamics similar?
Transitive property
2. What is thermal contact?
Two objects are said to be in thermal contact when they are in contact with each other in such a way that the transfer of energy by heat can occur between them.
1. When are two bodies in thermal equilibrium?
When they are in thermal contact and are at the same temperature
61. What is the change in entropy caused by melting 5.00 kg of ice at 0 °C ?
[ΔS=Q/T] 0°C+ 273= 273 K Q=mLf Q/T= 5(334 KJ--> 334000J)/273 = 6.11 X 10^3 J/K
62. What is the amount of heat required to cause a change of 35J/K in the entropy of a system at 400K?
[ΔS=Q/T] 35=Q/400K Q= 35(400) =1.4 X10^4 J
56. Ten joules are transferred by heat into a system, followed by another 20J. What is the change in the system's internal energy? What would be the difference in this change if 30J of energy were added by heat to the system at once?
[ΔU=Q-W] Q= 10+20= 30J 30J; the change in internal energy would be same even if the heat added the energy at once
55. Three hundred ten joules of heat enter a system, after which the system does 120J of work. What is the change in its internal energy? Would this amount change if the energy transferred by heat were added after the work was done instead of before?
[ΔU=Q-W] Q=310 W=120 ΔU= 310=120= 190 J 190J; this would not change even if heat added energy after the work was done
26. Eighty joules are added by heat to a system, while it does 20J of work. Later, 30J are added by heat to the system, and it does 40J of work. What is the change in the system's internal energy?
[ΔU=Q-W] Q=80 + 30 W= 20 + 40 ΔU=110-60= 50J
25. Some amount of energy is transferred by heat into a system. The net work done by the system is 50J, while the increase in its internal energy is 30J. What is the amount of net heat?
[ΔU=Q-W] ΔU= 30J W= 50J 30= Q-50 Q= 80J
70. Why does a bridge have expansion joints?
because the bridge expands and contracts with the change in temperature
60. How is it possible for us to transfer energy by heat from cold objects to hot ones?
by doing work on the system
thermal equilibrium
condition in which heat no longer transfers energy between two objects that are in contact; the two objects have the same temperature
Boltzmann constant
constant with the value k = 1.38×10−23 J/K, which is used in the ideal gas law
during expansion, increase in volume...
decreases the internal pressure of a system
34. What is conserved in the first law of thermodynamics?
energy
9. Give an example of entropy as experienced in everyday life.
filling a car tire with air
pressure
force per unit area perpendicular to the force, over which the force acts
37. In an engine, what is the unused energy converted into?
heat
7. The first law of thermodynamics helps us understand the relationships among which three quantities?
heat, work, and internal energy
during compression, decrease in volume...
increases the internal pressure of a system
33. Which of the following involves work done BY a system?
increasing internal energy
entropy
measurement of a system's disorder and how much energy is not available to do work in a system entropy formula= [ΔS=Q/T] (measured in J/k) *the more disorders a system is and the higher the entropy, the less of a system's energy is available to do work* *larger change in entropy @low temps* T= absolute temp Q= heat that transfers
ideal gas law
physical law that relates the pressure and volume of a gas to the number of gas molecules or atoms, or number of moles of gas, and the absolute temperature of the gas ideal gas law formula= PV=NkT k = 1.38×10−23 J/K (boltzmann constant) N= #of particles in the gas T= absolute temp P= pressure of gas V= volume it occupies
zeroth law of thermodynamics
states that if two objects are in thermal equilibrium, and a third object is in thermal equilibrium with one of those objects, it is also in thermal equilibrium with the other object
first law of thermodynamics
states that the change in internal energy of a system equals the net energy transfer by heat into the system minus the net work done by the system formula for first law of TD= [ΔU= Q-W] (measured in Joules {J}) Q= heat W= Work *humans and plants also do thermodynamics*
second law of thermodynamics
states that the total entropy of a system either increases or remains constant in any spontaneous process; it never decreases *heat transfers energy spontaneously from higher to lower temp objects*
internal energy
sum of the kinetic and potential energies of a system's constituent particles (atoms or molecules) (U)
examples of entropy
sun, mining, marbles, plants
8. Air freshener is sprayed from a bottle. The molecules spread throughout the room and cannot make their way back into the bottle. Why is this the case?
the entropy of the molecules increases
12.2: First Law of Thermodynamics: Thermal Energy and Work
-Pressure is the force per unit area over which the force is applied perpendicular to the area. -Thermal expansion is the increase, or decrease, of the size (length, area, or volume) of a body due to a change in temperature. -The ideal gas law relates the pressure and volume of a gas to the number of gas particles (atoms or molecules) and the absolute temperature of the gas. -Heat and work are the two distinct methods of energy transfer. -Heat is energy transferred solely due to a temperature difference. -The first law of thermodynamics is given as ΔU=Q−W, where ΔU is the change in internal energy of a system, Q is the net energy transfer into the system by heat (the sum of all transfers by heat into and out of the system), and W is the net work done by the system (the sum of all energy transfers by work out of or into the system). -Both Q and W represent energy in transit; only ΔU represents an independent quantity of energy capable of being stored. -The internal energy U of a system depends only on the state of the system, and not how it reached that state.
12.1: Zeroth Law of Thermodynamics: Thermal Equilibrium
-Systems are in thermal equilibrium when they have the same temperature. -Thermal equilibrium occurs when two bodies are in contact with each other and can freely exchange energy. -The zeroth law of thermodynamics states that when two systems, A and B, are in thermal equilibrium with each other, and B is in thermal equilibrium with a third system, C, then A is also in thermal equilibrium with C.
14. Oil is heated in a pan on a hot plate. The pan is in thermal equilibrium with the hot plate and also with the oil. The temperature of the hot plate is 150 °C . What is the temperature of the oil?
150 °C
21. Entropy never decreases in a spontaneous process. Give an example to support this statement.
A plant uses energy from the sun and converts it into sugar molecules by the process of photosynthesis.
71. Under which conditions will the work done by the gas in a system increase?
It will increase when a large amount of energy is added to the system, and that energy causes an increase in the gas's volume, its pressure, or both.
18. Air is pumped into a car tire, causing its temperature to increase. In another tire, the temperature increase is due to exposure to the sun. Is it possible to tell what caused the temperature increase in each tire? Explain your answer.
No, because the changes in energy for both systems are the same, and the cause of that change does not matter; the state of each system is identical.
formula for pressure
P=F/A unit is in pascal (Pa) 1 Pa=N/m^2
5. How does pressure-volume work relate to heat and internal energy of a system?
The energy added to a system by heat minus the change in the internal energy of that system is equal to the pressure-volume work done by the system.
41. A system consists of ice melting in a glass of water. What happens to the entropy of this system?
The entropy of the system increases.
17. A hydroelectric dam produces electricity by moving water from a reservoir fed by a river above through a turbine below. Consider the system to include the dam and the reservoir. If the turbine jams and stops producing electricity, what effect will this have on the internal energy of the system?
The internal energy would remain constant because work is no longer being done.
13. What are the necessary conditions for energy transfer by heat to occur between two bodies through the process of conduction?
They should be at different temperatures, and they should be in thermal contact.
59. A cold object in contact with a hot one never spontaneously transfers energy by heat to the hot object. Which law describes this phenomenon?
the second law of thermodynamics
6. On what does internal energy depend?
the state of the system
Pressure-Volume Work
the work that is done by the compression or expansion of a fluid. When there is a chance in volume and external pressure remains constant, pressure-volume work is taking place.
30. What thermodynamic principle forms the basis for our ability to measure temperature?
the zeroth law
If Q is positive...
then there is a net heat transfer into the system (Q adds energy) energy transferred by heat is positive energy or heat transferred out of the system is negative Qin - Qout= Q
If W is positive...
then there is a net work done by the system (W takes energy) the system doing work is positive any work done on the system is negative Wout-W in= W
