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Chapter 11

# Chapter 11 - Thermodynamics Covers a broad range of topics...

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Thermodynamics Covers a broad range of topics including: 1. The transfer of energy 2. The meaning and definition of heat 3. If a reaction is possible 4. How will changes in variables such as temperature and pressure affect a reaction Thermodynamics does not rely on an atomistic understanding of matter. It is as important to chemists as it is to biologists and engineers.

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Why is Thermodynamics Often Difficult for Chemists Because there is a fair amount of math involved and a lot of operational definitions to learn
Thermodynamics – Operational Definitions 1. A system – part of the universe of interest to us. Could be: a. Gas molecules confined in a closed box b. Gas molecules in 1cm3 within the closed box 2. A closed system – matter can neither leave or enter the system (1a is a closed system because gas phase molecules can not leave the system and nothing can enter) An open system – 1b is an open system (gas molecules can leave and enter) 3. An isolated system – exchanges neither matter or energy with the surroundings 4. The surroundings – the rest of the universe that can exchange matter or energy with the system

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Intensive and Extensive Properties Consider a system that comprises a gas contained within a fixed box. Gas Now imagine dividing the box into two subsystems What properties of the system are the same on both sides of the artificial line (Pressure, Temperature). These are intensive properties (the same in each subsystem) What properties of the system are the sum of the properties in each subsystem (Volume, Mass, Energy). These are extensive properties subsystem subsystem
Equilibrium When none of a system’s properties (e.g. temperature, pressure, volume) are changing with time the system is said to have reached equilibrium For a given quantity of material, thermodynamic equilibrium is fixed when any two of its independent properties are known (thus, for one mole of an ideal gas knowing the temperature and volume is enough to define the pressure since PV = nRT)

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Thermodynamic Process Change the thermodynamic state of the system. These changes may be: 1. Physical (e.g. change in the pressure applied to a gas or the boiling of water) or 2. Chemical (e.g. reaction of CaCO3 at 900K and 1atm to give CaO and CO2) In a thermodynamic process the system starts in one state (e.g. A) and ends in another (e.g. B)
Reversible and Irreversible Processes Consider gas confined within a piston. If the volume is suddenly expanded to a larger value of V2 then things such as the density are not uniform with the system and it can no longer be considered to be in equilibrium. This is an irreversible process . (1kg sand added to a piston as a sandbag) However, if the volume is expanded very slowly then at each point in the expansion the gas will be in equilibrium. This is a reversible process. Of course a reversible process can never be fully realized in practice but it can be approximated. (1 grain of sand added to a piston at a time)

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Reversible and Irreversible Processes An irreversible process can not be
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