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# chem lecture ch18

first law of thermodynamics The first law of thermodynamics states, that internal energy ( E ) may be transferred as heat or work, but can not be created or destroyed. Internal energy is defined as the sum of all the kinetic and potential energies of the particles of a system.
The expression for the change of the internal energy is? delta E = q + w q > 0 Heat is absorbed by the system q < 0 Heat is released by the system w > 0 Work is done on the system w < 0 Work is done by the system
state function of enthalpy H = E + P V at constant pressure.. delta H = qp
isothermal process a thermodynamic process , in which the temperature remains constant.
isobaric process a thermodynamic process in which the pressure stays constant.
spontaneous change a change that occurs by itself without continuous outside interference. Some of these changes occur were fast, whereas others can take years.
Entropy a measure of the number of equivalent ways to distribute energy in a system.
Entropy state function delta S = Sfinal - Sinitial ; delta S = SProducts - SReactants
factors that influence the change of entropy 1. volume 2. temperature 3.
the three factors that influence the spontaneity of processes are ? 1. Enthalpy change 2. Entropy change 3. Temperature
second law of thermodynamics whenever a spontaneous event happens in the universe, the total entropy of the universe increases. As a systems entropy can decrease, there must be a larger increase in entropy in a system undergoing a spontaneous change.
Gibbs free energy delta G = delta H - T *delta S
For a change to be spontaneous, delta G must be _______? negative
3rd law of thermodynamics at absolute zero, the entropy of a perfectly ordered pure sample equals zero
change of the standard entropy formula S° = (sum of S° of the products) - (sum of S° of the reactants)
The Clausius equation δq / T = ΔS
Gibbs free energy equation for reactants and products in a system ΔG [the Gibbs free energy change of the system] = ΔH [the enthalpy change] −T ΔS [the entropy change].
Hess’s law The value of H° for any reaction that can be written in steps equals the sum of the values of H° of each of the individual steps.
A process is called thermodynamically reversible if... its driving force is opposed by another force, that is just a little bit weaker.
When G° is positive... the position of the equilibrium lies close to the reactants and little reaction occurs by the time equilibrium is reached. The reaction will appear nonspontaneous.
When G° is negative... the position of the equilibrium lies close to the products and a large amount of products will have formed by the time equilibrium is reached. The reaction will appear spontaneous.
When G° = 0 ... the position of the equilibrium will lie about midway between reactants and products. The reaction will appear spontaneous whether it is started with pure reactants or pure products.
reaction quotient It is a function of the concentrations of the chemical species involved in a chemical reaction. In the special case that the reaction is at equilibrium, the reaction quotient is equal to the equilibrium constant.
Created by: jsherm82