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Chemistry and the material world 123.102 Unit 4, Lecture 1 Matthias Lein Magdeburg hemispheres (1650) Otto von Guericke 1602 – 1686 Germany Boyle's law: pV = const. p1V1 = p2V2 Joseph Louis Guy-Lussac 1778 – 1850, France Guy-Lussac's law: p/T = const. Robert Boyle 1627 – 1691, England p1T2 = p2T1 Charles' law: V/T = const. V1T2 = V2T1 Jaques Charles 1746 – 1823, France Robert Hooke 1635 – 1703, England Avogadro's law: V/n = const. V1/n1 = V2/n2 Amedeo Avogadro 1776 – 1856, Italy ideal gas law: pV = nRT p is the absolute pressure of the gas V is the volume of the gas n is the number of moles of the gas R is the universal gas constant T is the absolute temperature ● Chemical thermodynamics allows us to predict both the direction and the extent of spontaneous chemical and physical change under particular conditions using a property called the Gibbs free energy, G. Josiah Gibbs 1839 – 1903, United States ● ● Chemical reactions and physical changes almost always either absorb or release energy as heat. Energy may be distributed throughout a chemical system in a large number of different ways, some of which have significantly higher probabilities than others ● G = H – TS H enthalpy of the system – ● S entropy of the system – ● Function related to the heat absorbed or evolved by a chemical system Measure of number of ways energy is distributed throughout a chemical system T temperature in kelvin ΔG = ΔH – TΔS • ΔG allows us to determine whether a particular chemical reaction or physical change is spontaneous ● If ΔG < 0, the process is spontaneous ● If ΔG > 0, the process is nonspontaneous ● If ΔG = 0, the system is at equilibrium ● ● System refers to the particular chemical species being studied Surroundings are everything else • Universe refers to the system and the surroundings • Boundary defined as region across which heat flows ● Open systems – ● Closed systems – ● Can gain or lose mass and energy across their boundaries Can absorb or release energy, but not mass, across the boundary Isolated systems – Can not exchange matter or energy with their surroundings Example: Open System Example: Closed System Example: Isolated System (important: truly isolated systems do not exist) Today we covered: ● Introduction into correlations between pressure, volume, temperature and the number of moles for gases. ● Construction of the ideal gas law from these correlations. ● Description of all systems with the Gibbs free energy. ● Connection of spontaneous processes to the change in the Gibbs free energy. ΔG < 0 ΔG > 0 ΔG = 0 ● ● spontaneous non-spontaneous equilibrium Definition of a system, including the boundary and the surrounding. Open systems, closed systems, isolated systems