2: The First Law of Thermodynamics
- Page ID
- 456140
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- 2.1: Work and Heat
- Joule was able to show that work and heat can have the same effect on matter – a change in temperature! It would then be reasonable to conclude that heating, as well as doing work on a system will increase its energy content, and thus it’s ability to perform work in the surroundings. This leads to an important construct of the First Law of Thermodynamics: The capacity of a system to do work is increased by heating the system or doing work on it.
- 2.2: Pressure-Volume Work
- Work in general is defined as a product of a force FFF and a path element dsdsds. In the case of a cylinder, the movement of the piston is constrained to one direction, the one in which we apply pressure (\(P\) being force \(F\) per area \(A\)). We can therefore introduce the area of the piston, \(A\), and forget about the vectorial nature of force. This form of work is called pressure-volume (\(PV\)) work, and it plays an important role in the development of our theory.
- 2.3: Internal Energy and Enthalpy
- Unlike heat and work, energy is a state function. That is, it is independent of the path taken. Any path can be used to calculate the change in energy between two states.
- 2.4: Ideal Gas Processes
- It is convenient to use the work of expansion to exemplify the difference between work that is done reversibly and that which is done irreversibly. The example of expansion against a constant external pressure is an example of an irreversible pathway. It does not mean that the gas cannot be re-compressed. It does, however, mean that there is a definite direction of spontaneous change at all points along the expansion.
- 2.5: Exact and Inexact Differentials
- Because thermodynamics is kind enough to deal in a number of state variables, the functions that define how those variable change must behave according to some very well determined mathematics. This is the true power of thermodynamics!
- 2.6: The Joule Experiment
- Joule's experiment concluded that dq=0 (and dT=0) when a gas is expanded against a vacuum. And because dV>0 for the gas that underwent the expansion into an open space, the internal pressure must also be zero!
- 2.7: Calorimetry
- As chemists, we are concerned with chemical changes and reactions. The thermodynamics of chemical reactions can be very important in terms of controlling the production of desired products and preventing safety hazards such as explosions. As such, measuring and understanding the thermochemistry of chemical reactions is not only useful, but essential!
- 2.E: First Law of Thermodynamics Exercises
- Exercises for Chapter 3 "First Law of Thermodynamics" in Fleming's Physical Chemistry Textmap.