Day 4: Kinetic Theory and PV Diagrams

 Quiz Problem

 We started the class with a pop-quiz. The quiz was about using the formula Q = m*c*ΔT and Q = mL to find the mass of water. There are two uncertainties: temperature and time. And if the data was correct, the final mass would be higher than we got.

Work Done By an Expanding Gas

Then we started an experiment about work done by an expanding gas. By drawing the x vs. Force graph, we learned that the work done is the area under the curve on the graph.

When we put the flask in hot water, the volume of air in the syringe will be bigger while when we put the flask in cold, the volume of air in the syringe will be smaller.

First Law of Thermodynamic Activity

Then we defined the equation of the first law of thermodynamics which is ΔEint equals Q - W.

We also did two conditional of Internal energy where there is no Q (heat) or no W (work).

This is the example problem of first thermodynamics problem we calculated in class.

2D Molecular Motion

Every purple bubble represents a molecule, as the temperature or pressure goes up, the molecules will move faster.

Kinetic Theory

In this picture, we found the speed square f a molecule to be Vt^2 = 3Vx^2 since Vx = Vy = Vz.

By plugging to the formula P = F/A = NmVx^2/V we found that P = NmV^2/3V

Then we used the formula PV = NKbT to find that T is 2/3 E/Kb. And Vrms = squr(3KbT/m).

Also, in this photo, we found the T_f ^3/2 V_f = T_i ^3/2 V_i

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Fire Syringe

Then we did a fire syringe experiment and a problem to solve for Tf using the above formula and got 711 K

Conclusion

In conclusion, we learned the first law of thermodynamics is ΔEint = Q - W, and when pressure is constant, W = (v2 - v1). Then, we looked at the molecular model and it's relationship to pressure and temperature. Also, we found a relationship between Temperature and volume for adiabatic expansions which is T_f ^3/2 V_f = T_i ^3/2 V_i.