5. r ész
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5. rész
Termodinamikai alapfogalmakElektrokémiaReakciókinetika
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Termodinamikai alapokEntalpia: H = U + pV; reakcióhő nyitott edényben, vagyis ha p = const.
Entalpiadiagramok:
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A folyamatok iránya: entrópia
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WikipediaMicroscopic definition of entropy (statistical mechanics)
In statistical thermodynamics the entropy is defined as the number of microscopic configurations that result in the observed macroscopic description of the thermodynamic system:
S = kB lnwhere
kB is Boltzmann’s constant 1.38066×10−23 J K−1 and is the number of microstates corresponding to the observed thermodynamic macrostate.
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Szabadentalpia: G = H – TS G minimuma definiálja az EGYENSÚLYT
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Elektrokémia Galváncellák
Fémlemez vízbe mártva: bizonyos tendenciával pozitív ionok mennek az oldatba; egy idő után a lemez negatív töltése már nem engedi, dinamikus egyensúly alakul ki. Az ábra azt illusztrálja, hogy a Mg nagyobb hajlammal oldódik be ...
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Elektródpotenciál: a hidrogénelektróddal szemben mért e.m.e.
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Egy üzemanyag-cella
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Elektrolízis: réz raffinálása
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Reakciókinetika: reakciók sebessége, mechanizmusa
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Ütközési elmélet, az Arrhenius-egyenlet.
k = A exp (-Ea/RT)
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2. http://www.chemgapedia.de/vsengine/vlu/vsc/en/ch/12/oc/vlu_organik/alkene/hydrierung.vlu/Page/vsc/en/ch/1
Details of the mechanism of catalytic hydrogenation are not known. Probably, both hydrogen and alkene are bound to the surface of the catalyst activating the π bond of the alkene as well as the σ bond of the hydrogen. The alkane product only leaves the surface of the catalyst after the transfer of hydrogen (deuterium) atoms to the alkene is completed.
KatalízisPéldául: Hidrogénezés
The reaction rate of hydrogenation depends on the degree of substitution at the double bond. Higher-substituted alkenes show a lower reaction rate than less substituted. This fact can be explained by larger steric hindrance as well as better stabilization of the π bond in higher-substituted alkenes. Therefore, selective hydrogenation of differently substituted double bonds is often possible. For an overview of alkene hydrogenation click here.
Fig.3Mechanism of catalytic hydrogenation