6016Lect#8Micro&amp;Biochem_2013

# Two half cells is an electrochemical cell a salt

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Two half-cells is an electrochemical cell. A salt bridge allows ions to pass while keeping the solutions from mixing. The electromotive force generated by the cell is a measure of the driving force of the chemical reaction occurring in the half-cell solution, ie. a measure of the chemical potential or free energy of the reaction. Joule = measure of electrical energy = energy of flow of 1 ampere in 1 second against an emf of 1 volt = Elt [volt coulomb] OR [joule] Ohm's law is E = IR E = emf [volts] I = current [amperes] R = resistance [ohms] Joule represent work and volts represent force. Amperes are rate of flow of electrons [e / T] or [coulomb/sec] Coulomb is # of electrons per sec (1/96500th of a Faraday) A Faraday is an equivalent of electrons. Some important definitions : energy - the capacity for doing work work - the product of force and the displacement of an object caused by that force. Measured in joules [1N (force) times displacement, meters: Nm]; Newtons are kg m/sec 2 from Weight (force)=mass X acceleration of gravity power - the rate of doing work (units energy per unit time). Some unit expressions describing: Force [mass length/time 2 ] Newtons Energy [force length (displacement)] Btu Calorie Joules kWhr Power [energy/time] Watt Joules/sec Btu/hr Note : Since W = E/time, then kWhr = E it is an E term Power (ie. E/time) : 1 W = 1 J/s = 3.412 BTU/hr Electrical energy expended to change 1 mole of chemical is zEF, where z => is the # of electron-equivalents per mole

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