Chapter 19

# Chapter 19 - Chapter 19 – Thermodynamics and equilibrium...

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Unformatted text preview: Chapter 19 – Thermodynamics and equilibrium thermodynamics is the study of the relationship between heat and other forms of energy involved in a chemical or physical process – this will allow you to determine what direction any reaction will run in, and where the reaction will sit at equilbrium – in other words, is a specific reaction likely to go, and if so, what is the composition of the reaction mixture once equilibrium is achieved there are 3 fundamental laws of thermodynamics, can state them flippantly: 1 – the best you can ever do is break even 2- the only time you can break even is at absolute zero 3- you can never reach absolute zero go back to the first law, which is essentially conservation of energy in a true thermodynamic system – need to reconsider the internal energy U, which we discussed in chapter 6 – the internal energy U is the sum of the kinetic and potential energies of the particles making up the system – the kinetic energy includes the motion of the electrons and molecules of the system – the potential energy includes the attractive forces of the bonding of the atoms and the molecules internal energy is a state function , which means its value depends only on its present state and not how it got there – depends on variables such as temperature and pressure – when a system changes from one state to another, can describe the change in internal energy ∆ U, as ∆ U = Uf - Ui normally will measure changes in internal energy for a system, rather than the absolute values of U – these are determined by observing the exchange of energy between what we define as “the system” and its “surroundings” – the energy can take one of two forms, heat or work – heat is the energy that goes into or out of a system because of a difference in temperature between the system and its surroundings work is the energy that the system does to move an object a distance i.e., a piston, distance d by using a force F – work equals force X distance Figure 18.2 need to make the value of the heat, q, is defined as + if heat passes from the surroundings into the system or – if heat passes from the system to the surroundings if the gas in figure 18.2 gains energy from the surroundings (q is +) so now the temperature of the gas increases, and if the piston is allowed to move (i.e, constant pressure), the gas will expand due to the increase in temperature and so do work equal to the force of gravity on the piston times the distance the piston moves – since the piston is defined as part of the surroundings,...
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Chapter 19 - Chapter 19 – Thermodynamics and equilibrium...

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