Lab 10 Thermodynamics PHY250L
Student Name:
Access Code (located on the underside of the lid of your lab kit):
Lab Report Format Expectations
Utilize college level grammar and formaṄng when answering text based questions.
Report all equations in a proper mathematical format, with the correct signs and symbols.
Submissions with incomplete or improperly formatted responses may be rejected.
Pre-Lab Questions
The first law of thermodynamics discusses the interplay between heat and work and how they come
together to describe the internal energy changes of a system undergoing a thermodynamic process.
Importantly, though, the first law of thermodynamics is, at its core, a statement about the conservation
of energy. Energy cannot be created or destroyed. it cannot vanish into nothingness or spontaneously
appear. This law can be stated mathematically as:
ΔU =Q−W
1. The first law of thermodynamics, expressed as ΔU = Q − W, states that the change in internal
energy (ΔU) of a system is equal to the heat added to the system (Q) minus the work done by
the system (W). This law represents the conservation of energy, meaning energy cannot be
created or destroyed—only transferred or transformed. If heat is added to a system and no
work is done, the internal energy increases. If the system does work on its surroundings, its
internal energy decreases accordingly.
Note the negative (-) sign for work, W, in the above equation. The choice of a negative or a positive sign
depends on the way you describe the system.
Explain when the work term would have a positive magnitude and when it would have a negative
magnitude. In your response, utilize the work equation, which is below, to justify your response.
W =−Pext x ΔV
2. According to the equation W = -Pext × ΔV, work is positive when the system is compressed (ΔV is
negative), because energy is added to the system. Work is negative when the system expands
(ΔV is positive), because the system uses energy to push against external pressure.
, Lab 10 Thermodynamics PHY250L
3. The second law of thermodynamics states that the entropy of an isolated system can never
decrease over time, and is constant if and only if all processes are reversible. Isolated systems
spontaneously evolve towards thermodynamic equilibrium—the state of maximum entropy of
the system. More simply put: the entropy of the universe (the ultimate isolated system) only
increases and never decreases.
Explain, using probability theory and the concepts of macrostates and microstates, why entropy
increases. Be specific and state your response with enough detail that your level of
understanding is clearly demonstrated.
Entropy increases because there are more possible microstates (ways to arrange particles) than
macrostates (overall observable conditions). According to probability theory, systems naturally
move toward the most probable state—which is the one with the highest number of
microstates. Since there are many more disordered arrangements than ordered ones, isolated
systems tend to evolve toward disorder, increasing entropy over time.
4. When you put a few drops of food coloring in water, the molecules of food coloring will
eventually diffuse throughout the whole glass. Use the Second Law of Thermodynamics to
explain why the entropy of the diffused food coloring is greater than when you initially drop the
food coloring into the water. Your response should tie in the same concepts of microstates,
macrostates and entropy that you described in your response to Question 4, above.
When food coloring is first added to water, the molecules are concentrated in one area—a low-
entropy state with fewer possible microstates. As the molecules diffuse throughout the water,
they spread out and occupy more space in random ways, increasing the number of microstates.
According to the Second Law of Thermodynamics, the system becomes more disordered and
moves toward a higher-entropy macrostate. This is because a uniform mixture has many more
possible microstates than a concentrated one.
Student Name:
Access Code (located on the underside of the lid of your lab kit):
Lab Report Format Expectations
Utilize college level grammar and formaṄng when answering text based questions.
Report all equations in a proper mathematical format, with the correct signs and symbols.
Submissions with incomplete or improperly formatted responses may be rejected.
Pre-Lab Questions
The first law of thermodynamics discusses the interplay between heat and work and how they come
together to describe the internal energy changes of a system undergoing a thermodynamic process.
Importantly, though, the first law of thermodynamics is, at its core, a statement about the conservation
of energy. Energy cannot be created or destroyed. it cannot vanish into nothingness or spontaneously
appear. This law can be stated mathematically as:
ΔU =Q−W
1. The first law of thermodynamics, expressed as ΔU = Q − W, states that the change in internal
energy (ΔU) of a system is equal to the heat added to the system (Q) minus the work done by
the system (W). This law represents the conservation of energy, meaning energy cannot be
created or destroyed—only transferred or transformed. If heat is added to a system and no
work is done, the internal energy increases. If the system does work on its surroundings, its
internal energy decreases accordingly.
Note the negative (-) sign for work, W, in the above equation. The choice of a negative or a positive sign
depends on the way you describe the system.
Explain when the work term would have a positive magnitude and when it would have a negative
magnitude. In your response, utilize the work equation, which is below, to justify your response.
W =−Pext x ΔV
2. According to the equation W = -Pext × ΔV, work is positive when the system is compressed (ΔV is
negative), because energy is added to the system. Work is negative when the system expands
(ΔV is positive), because the system uses energy to push against external pressure.
, Lab 10 Thermodynamics PHY250L
3. The second law of thermodynamics states that the entropy of an isolated system can never
decrease over time, and is constant if and only if all processes are reversible. Isolated systems
spontaneously evolve towards thermodynamic equilibrium—the state of maximum entropy of
the system. More simply put: the entropy of the universe (the ultimate isolated system) only
increases and never decreases.
Explain, using probability theory and the concepts of macrostates and microstates, why entropy
increases. Be specific and state your response with enough detail that your level of
understanding is clearly demonstrated.
Entropy increases because there are more possible microstates (ways to arrange particles) than
macrostates (overall observable conditions). According to probability theory, systems naturally
move toward the most probable state—which is the one with the highest number of
microstates. Since there are many more disordered arrangements than ordered ones, isolated
systems tend to evolve toward disorder, increasing entropy over time.
4. When you put a few drops of food coloring in water, the molecules of food coloring will
eventually diffuse throughout the whole glass. Use the Second Law of Thermodynamics to
explain why the entropy of the diffused food coloring is greater than when you initially drop the
food coloring into the water. Your response should tie in the same concepts of microstates,
macrostates and entropy that you described in your response to Question 4, above.
When food coloring is first added to water, the molecules are concentrated in one area—a low-
entropy state with fewer possible microstates. As the molecules diffuse throughout the water,
they spread out and occupy more space in random ways, increasing the number of microstates.
According to the Second Law of Thermodynamics, the system becomes more disordered and
moves toward a higher-entropy macrostate. This is because a uniform mixture has many more
possible microstates than a concentrated one.
