2
Physics thermodynamics conceptual questions with verified detailed || || || || || || ||
answers
Define a thermodynamic system and its environment - ✔✔A thermodynamic system is an
|| || || || || || || || || || || || ||
object or set of objects considered to be a distinct physical entity to or from which energy is
|| || || || || || || || || || || || || || || || || ||
added or removed. The surrounding of the system is its environment
|| || || || || || || || || ||
In what two ways can the internal energy of a system be increased - ✔✔This means that
|| || || || || || || || || || || || || || || || ||
internal energy of a system can be increased by adding heat into the system or by
|| || || || || || || || || || || || || || || ||
performing work on the system. || || || ||
For each of the following, which thermodynamic quantities (delta u, q, w) have values equal
|| || || || || || || || || || || || || ||
to zero?
|| ||
A- an isothermal process
|| || ||
B- an adiabatic process
|| || ||
C- an isovolumetric process - ✔✔A- since the temperature doesn't change the internal
|| || || || || || || || || || || || ||
energy of the system doesn't change. Delta U=0
|| || || || || || || ||
B- no heat is added or removed from the system Q=0
|| || || || || || || || || ||
C- the volume of the system doesn't change so there is no work done on or by the system.
|| || || || || || || || || || || || || || || || || || ||
W=p delta v= 0 || || ||
When an ideal gas expands adiabatically it does work in its surroundings. Describe the
|| || || || || || || || || || || || || ||
various transfers of energy that take place - ✔✔When an ideal gas expands adiabatically,
|| || || || || || || || || || || || || ||
there is no transfer of heat so Q=0.
|| || || || || || || ||
Using the first law of thermodynamics: delta U=Q-W.
|| || || || || || || ||
The work done by the gas is positive which implies that the change in internal energy is
|| || || || || || || || || || || || || || || || ||
negative so in this case the internal energy of the gas is transferred to its surroundings
|| || || || || || || || || || || || || || ||
, 2
In each of the cases, trace the chain of energy transfers (as heat or work) as well as changes
|| || || || || || || || || || || || || || || || || || ||
in internal energy
|| || ||
A- you rub your hands together to warm them in a cold day, and they soon become cold
|| || || || || || || || || || || || || || || || || ||
again
B- a hole is drilled into a block of metal. When a small amount of water is placed in the
|| || || || || || || || || || || || || || || || || || || ||
drilled hole, steam rises from the hole - ✔✔A-When you rub your hands, you perform work
|| || || || || || || || || || || || || || || ||
against friction and during that process heat is generated. Thus work is converted into heat
|| || || || || || || || || || || || || || ||
energy. After that heat is transferred to the surroundings by conduction and convection of
|| || || || || || || || || || || || || ||
air and the hands become cold.
|| || || || ||
B- during the drilling process the drill machine preforms work on the block of metal which
|| || || || || || || || || || || || || || || ||
converts into heat and increases its temperature. This temp is typically about 100 degrees
|| || || || || || || || || || || || || ||
celsius, the boiling point of water. Now if a small amount of water is placed in the hole, the
|| || || || || || || || || || || || || || || || || || ||
water will absorb the heat and some amount of water will become vapor. In this case heat is
|| || || || || || || || || || || || || || || || || ||
transferred from the metal plate to the water molecules and the internal energy of water
|| || || || || || || || || || || || || || ||
increases.
Paint from an aerosol can is sprayed continuously for 30 s. The can was initially at room
|| || || || || || || || || || || || || || || || ||
temperature but now feels cold to the touch. What type of thermodynamic process occurs || || || || || || || || || || || || || ||
for a small sample of gas as it leaves the high pressure interior of the can and moves to the
|| || || || || || || || || || || || || || || || || || || ||
outside atmosphere. - ✔✔As a small sample of gas comes out of the aerosol can from high
|| || || || || || || || || || || || || || || || ||
pressure region to the outside atmospheric pressure, its volume increases rapidly. The
|| || || || || || || || || || || ||
process happens so fast that the gas doesn't get chance to exchange any heat with the
|| || || || || || || || || || || || || || || ||
surroundings. Thus it is an adiabatic process. Since the process is adiabatic and it's volume || || || || || || || || || || || || || || ||
increases so that W=P delta V >0 from the first law of thermodynamics we have delta u =
|| || || || || || || || || || || || || || || || || ||
Q- W < 0. Thus the internal energy of the gas decreases which means that the temperature
|| || || || || || || || || || || || || || || || ||
of the gas will go down. This is why the can feels cold after it is sprayed
|| || || || || || || || || || || || || || || ||
The can if spray paint in the previous question is set aside for an hour. During this time the
|| || || || || || || || || || || || || || || || || || ||
contents of the can return to room temperature. What type of thermodynamic process takes
|| || || || || || || || || || || || || ||
place in the can during the time the can is not in use? - ✔✔The cold aerosol can when left
|| || || || || || || || || || || || || || || || || || || ||
aside, heat in transferred into it from its surrounding due to the temperature difference. In
|| || || || || || || || || || || || || || ||
this process the temperature of the can slowly increases and finally the can reaches the
|| || || || || || || || || || || || || || ||
room temperature. Since during the process the volume of the gas doesn't change, it is an
|| || || || || || || || || || || || || || || ||
isovolumetric process. ||
Physics thermodynamics conceptual questions with verified detailed || || || || || || ||
answers
Define a thermodynamic system and its environment - ✔✔A thermodynamic system is an
|| || || || || || || || || || || || ||
object or set of objects considered to be a distinct physical entity to or from which energy is
|| || || || || || || || || || || || || || || || || ||
added or removed. The surrounding of the system is its environment
|| || || || || || || || || ||
In what two ways can the internal energy of a system be increased - ✔✔This means that
|| || || || || || || || || || || || || || || || ||
internal energy of a system can be increased by adding heat into the system or by
|| || || || || || || || || || || || || || || ||
performing work on the system. || || || ||
For each of the following, which thermodynamic quantities (delta u, q, w) have values equal
|| || || || || || || || || || || || || ||
to zero?
|| ||
A- an isothermal process
|| || ||
B- an adiabatic process
|| || ||
C- an isovolumetric process - ✔✔A- since the temperature doesn't change the internal
|| || || || || || || || || || || || ||
energy of the system doesn't change. Delta U=0
|| || || || || || || ||
B- no heat is added or removed from the system Q=0
|| || || || || || || || || ||
C- the volume of the system doesn't change so there is no work done on or by the system.
|| || || || || || || || || || || || || || || || || || ||
W=p delta v= 0 || || ||
When an ideal gas expands adiabatically it does work in its surroundings. Describe the
|| || || || || || || || || || || || || ||
various transfers of energy that take place - ✔✔When an ideal gas expands adiabatically,
|| || || || || || || || || || || || || ||
there is no transfer of heat so Q=0.
|| || || || || || || ||
Using the first law of thermodynamics: delta U=Q-W.
|| || || || || || || ||
The work done by the gas is positive which implies that the change in internal energy is
|| || || || || || || || || || || || || || || || ||
negative so in this case the internal energy of the gas is transferred to its surroundings
|| || || || || || || || || || || || || || ||
, 2
In each of the cases, trace the chain of energy transfers (as heat or work) as well as changes
|| || || || || || || || || || || || || || || || || || ||
in internal energy
|| || ||
A- you rub your hands together to warm them in a cold day, and they soon become cold
|| || || || || || || || || || || || || || || || || ||
again
B- a hole is drilled into a block of metal. When a small amount of water is placed in the
|| || || || || || || || || || || || || || || || || || || ||
drilled hole, steam rises from the hole - ✔✔A-When you rub your hands, you perform work
|| || || || || || || || || || || || || || || ||
against friction and during that process heat is generated. Thus work is converted into heat
|| || || || || || || || || || || || || || ||
energy. After that heat is transferred to the surroundings by conduction and convection of
|| || || || || || || || || || || || || ||
air and the hands become cold.
|| || || || ||
B- during the drilling process the drill machine preforms work on the block of metal which
|| || || || || || || || || || || || || || || ||
converts into heat and increases its temperature. This temp is typically about 100 degrees
|| || || || || || || || || || || || || ||
celsius, the boiling point of water. Now if a small amount of water is placed in the hole, the
|| || || || || || || || || || || || || || || || || || ||
water will absorb the heat and some amount of water will become vapor. In this case heat is
|| || || || || || || || || || || || || || || || || ||
transferred from the metal plate to the water molecules and the internal energy of water
|| || || || || || || || || || || || || || ||
increases.
Paint from an aerosol can is sprayed continuously for 30 s. The can was initially at room
|| || || || || || || || || || || || || || || || ||
temperature but now feels cold to the touch. What type of thermodynamic process occurs || || || || || || || || || || || || || ||
for a small sample of gas as it leaves the high pressure interior of the can and moves to the
|| || || || || || || || || || || || || || || || || || || ||
outside atmosphere. - ✔✔As a small sample of gas comes out of the aerosol can from high
|| || || || || || || || || || || || || || || || ||
pressure region to the outside atmospheric pressure, its volume increases rapidly. The
|| || || || || || || || || || || ||
process happens so fast that the gas doesn't get chance to exchange any heat with the
|| || || || || || || || || || || || || || || ||
surroundings. Thus it is an adiabatic process. Since the process is adiabatic and it's volume || || || || || || || || || || || || || || ||
increases so that W=P delta V >0 from the first law of thermodynamics we have delta u =
|| || || || || || || || || || || || || || || || || ||
Q- W < 0. Thus the internal energy of the gas decreases which means that the temperature
|| || || || || || || || || || || || || || || || ||
of the gas will go down. This is why the can feels cold after it is sprayed
|| || || || || || || || || || || || || || || ||
The can if spray paint in the previous question is set aside for an hour. During this time the
|| || || || || || || || || || || || || || || || || || ||
contents of the can return to room temperature. What type of thermodynamic process takes
|| || || || || || || || || || || || || ||
place in the can during the time the can is not in use? - ✔✔The cold aerosol can when left
|| || || || || || || || || || || || || || || || || || || ||
aside, heat in transferred into it from its surrounding due to the temperature difference. In
|| || || || || || || || || || || || || || ||
this process the temperature of the can slowly increases and finally the can reaches the
|| || || || || || || || || || || || || || ||
room temperature. Since during the process the volume of the gas doesn't change, it is an
|| || || || || || || || || || || || || || || ||
isovolumetric process. ||
