Configuration Work This is the work done in a reversible process given by the product of some intensive variable (y) and the change in some extensive variable (X). The most general case would be: đW is called the configuration work; it is an inexact differential, i.e. work is not a state variable. The amount of work done changing the configuration of a system from one state to another depends on how the work is done, i.e. on the path taken between the final and initial states. The path must be specified in order to calculate work via integration. By convention, đW is the work done on ‘the system’. Thus, as an example, đW is positive when a gas is compressed. I explained why configuration work is inexact on the previous slide. Stress the convention that positive work is work done BY the system.

Configuration Work This is the work done in a reversible process given by the product of some intensive variable (y) and the change in some extensive variable (X). The most general case would be:

Dissipative Work Examples: Stirring Resistive electrical heating This is the work done in an irreversible process; it is always done ‘on the system’. Total work is the algebraic sum any configuration work and any dissipative work. If a process is reversible, then dissipation is necessarily zero. Examples: Stirring Resistive electrical heating Frictional work Plastic deformation Many chemical reactions There are some simple examples here: work done by a battery attached to a resistor, i2R; does not matter which way the current flows, the battery always ends up doing positive work. Not surprisingly, this work is converted to heat energy in the resistor and lost irreversibly to the surroundings. Friction F dot v; when you reversse v, F reverses as well, so the sign of the work remains unchanged.

Joule’s apparatus for measuring the mechanical equivalent of heat 1 cal = 4.184 J will raise temperature of water by 1 C (14.5 C to 15.5 C)

More on specific heat Using the first law, it is easily shown that: Finding a similarly straightforward expression for cP is not as easy, and requires knowledge of the state equation. These are far more useful expressions than the original definition of specific heat. For an idea gas, the internal energy depends only on the temperature of the gas T. Therefore,