Pre-Lab Questions
1. The first law of thermodynamics discusses the interplay between heat and work and how they
come together to describe the internal
... [Show More] 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
Explain howthis equation demonstrates boththe first lawof thermodynamics∧the concept of conservationoThe equation is used to describe that energy cannot be created or destroyed. One form of
energy is transferred to another form, and relates to the kinetic energy of a falling object being
brought to it potential energy. Whats unique about this equation is that the change in internal
energy is equal to the added heat of the system
2. 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 The work term would be positive when the system spreads and pushes against
external pressure.When this happens the change in (V) becomes positive. When the change in
volume becomes positive the pressure becomes negative because the system losses energy. On
the other hand, the change in volume will be negative if the system is compressed by its
surroundings. This then turn the pressure from a negative to a positive indication that the
system is absorbing energy. The result of this makes (W) work within the system have a negative
magnitude.
Lab 10 Thermodynamics PHY250L
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 in an isolated system because there are more microstates involved with the
system. A gas tends to have more microstates and more molecules are randomly in motion.
Macrostate have a lower entropy because the molecules are more organized. Solids have the
most macrostates because the water molecules are frozen. Liquids can be both because the
molecules of a liquid can be spread apart or put back together. If an object changes in
temperature, it will have more macrostates due to the thermal energy that is placed on it. It is
normal for a Entropy to spontaneously move towards the macrostate that has the highest
number of accessible microstates, which is similar to the state of the highest entropy. This is
because it is more common for molecules to be at room temperature unless changes in
temperature or a specific device is able to change the form of the number of macro and
microstates in a object. [Show Less]