2nd Law of Thermodynamics 3/10/2014

Today we started off by analyzing a general heat engine cycle. This is a Pressure v.s Volume graph with our calculated values.  As the cycle transform from one stage to the next, the pressure and volume of the system changes affecting either the internal energy E via heat transfer Q or just Work being done.  The different paths plays a role whether work is being done by the gas or work being done on the gas. The paths in which heat was transferred to the gas and in which heat was transferred from the gas are noted as followed:

This is just an ideal theoretical analysis of a SIMPLE GAS CYCLE to give us a better idea of how real heat engines use gases as a working medium.  This cycle is not realistic.

Simple Gas Cycle

We then brought theoretical into real life.  Prof Mason demonstrated an experiment that utilizes a glass syringe attached to a flask filled with air.  The flask is then put into a beaker full of hot water and cold water in order to see how the volume and the pressure of the system changes. First, as weight (apple) is placed on the syringe, the volume decreases as pressure increases.  Then, as the gas is heated with pressure increasing, the volume expands.   Next, as the weight is removed, the pressure decreases while the volume raises some more.  Finally, as everything cools off, the pressure and volume returns to its initial state.

Prof Mason working on the experiment as logger pro records the relevant data.

In order to further understand these processes, we created a Pressure-Volume Diagram in order to see how the cycle works.

The theoretical analysis of a heat engine that shows the process of a isobaric and isovolumetirc system.  The change in internal energy, heat, and work was calculated in the above picture based on the pressure volume and temperature given at each point. 

Then we did some activities on ActivPhysics as follows the simulation instructions for Questions 6, 7, and 8, we were  and answer the questions provided.:

Queston 6: The change in temperature was monitored in order to calculate the constant pressure molar heat capacity. Our rough estimations said that Cp=20.4J/(mol*K).

Question 7: The change in temperature from 200K to 800K was monitored in order to calculate the constant pressure molar heat capacity. Our rough estimations said that Cp=20.8J/(mol*K).

Question 8 shows the derivation of the constant pressure molar heat capacity from the change in the internal energy of a isobaric process. 

Last but not least, we were given an analysis of a Carnot engine cycle.  This is similar to the simple cycle but quite different due to its shape and most importantly, the different processes: The paths from A to B and from C to D were both isothermal expansions whereas the path from B to C was an adiabatic expansion, and the path from D to A was an adiabatic compression.  Following is our calculations:

Carnot Cycle with temperatures and internal energies at each point, as well as the equations to use for the rest of the work.  As shown the variables that we needed to find such as Change in internal energy, heat, and work for in between each point.