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Chem 112 Exam AID Course Pack

So with the increase in acetate anion the acidbase

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Unformatted text preview: er) [products]>>>[reactants] indicating a reaction that goes close to completion similarly if K is small 0.001 [products]<<<[reactants] indicating that reaction doesn’t go that well in that direction • If K=1 the concentrations of both products and reactants are close to equal Keq can also be described in terms of partial pressure if the reaction contains gaseous species. Instead of using concentrations as before we will replace them with the partial pressures of the gasses. KP (K using partial pressures) is related to KC (K using concentrations) by this equation: (R is the ideal gas constant and T is temperature in Kelvin) • ( c + d )−( a + b ) In addition to KP KC there is a thermodynamic equilibrium constant represented by K K P = KC (RT ) • € Ethan Newton & Barry Zhang for SOS Winter 2012 42 o o o K is a unit less constant found by using ratios of effective partial pressures to a reference pressure of 1.0atm (or using concentrations with a reference concentration of 1.0mol/L. These ratios are called activities Recall that at any temperature ΔG o = ΔH o − TΔS o can be calculated for substances in their standard states For a reaction (ex. A+Bà༎C )where the molecules involved are NOT in their standard c ⎛ྎ ⎞ྏ € ln ⎜ྎ [C] ⎟ྏ and at equilibrium ΔG = 0 states ΔG = ΔG + RT a b ⎝ྎ [A] [B] ⎠ྏ o and € [C ]c = K [A]a [B]b € ( − ΔG o / RT ) Therefore: ΔG o = − RT ln K rearranged to K = e € • We use the thermodynamic equilibrium constant because it can be calculated from ΔG o (Which is from ΔH o and ΔS o) which means the extent of equilibrium can be found using € € thermodynamic data (no experiments required) Relative Activity € The activity of a substance refers to the effectiveness of a substance in a reaction to influence € € equilibrium. • The relative activity is the activity relative to activity in standard state. • Standard sate activities for solutions is 1.0mol/L and for gasses is 1.0atm (*note: in this course we will assume that all systems are ideal so since both of these values are 1 when you calculate activities when finding K it doesn’t change the concentration or pressure values (dividing by one) but rather cancels out the units) o In non- ideal solutions different parts of the solution may interact with each other and not be available to affect equilib...
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