Chem Chapter 3

-The study of energy and its relationship to macroscopic properties of chemical systems. Thermodynamic functions are based on probabilities and are valid only for systems composed of a large number of molecules.

-Into a system and its surroundings. The system is the macroscopic body under study, surroundings are everything else.

What are the three types of systems?

-A state is the physical condition of a system described by a specific set of thermodynamic values.

-Extensive and intensive properties. Extensive properties are proportional to the size of a system. Intensive properties are independent of the size of a system. If you combine two identical systems and a property is the same for both the single system and combined system, that property is intensive. If a property doubles when the systems are combined, the property is extensive. If you divide one extensive property by another, the result is an intensive property.

-Volume (V) and number of moles (n) are examples of extensive properties.

-Pressure (P) and temperature (T) are examples of intensive properties.

-State functions (state function are properties) are pathway independent. State properties describe the state of a system. In other words the change in a state property going from one state to another is the same regardless of the process via which the system was changed.

-Properties that do not describe the state of a system, but depend upon the pathway used to achieve any state. Work and heat are examples of path functions.

What are the only two ways to transfer energy between systems?

-Heat is the natural transfer of energy from a warmer body to a cooler body. Any energy transfer that is NOT work is heat (q).

-Convection, conduction, and radiation.

-Conduction is the thermal energy transfer through the collision of molecules. Conduction requires direct physical contact. In conduction, higher energy molecules of one system transfers its energy to the lower energy molecules of another system via molecular collision.

-An objects ability to conduct heat is called its thermal conductivity (k). The thermal conductivity (k) of an object depends upon its composition and to a lesser extent its temperature. -A slab of a given substance with face area A, length L, and thermal conductivity k will conduct heat Q from a hot body at temperature T_h to a cold body temperature T_c in an amount of time t. Q/t = kA((T_h-T_c)/L) ---> Thermal Conductivity. Q/t = heat flow or heat current (I).

-The rate of heat flow would be constant. -If a series of slabs were lined up end to end between hot and cold reservoirs, the rate of heat flow, Q/t, would be the same in all slabs even if they each had different lengths, thicknesses, and different thermal conductivities.