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# CHEM 126 Chapter 17

### CHEM 126 Final

relationship between forward and reverse rexn rates at equilibrium rate(forward) = rate(reverse)
expression for equilibrium constant (Keq) [C]c*[D]d/[A]a*[B]b = Keq * all elements at eq
expression for reaction quotient (Q) [C]c*[D]d/[A]a*[B]b = Q * all elements at t (point in time)
solids/liquids in equilibrium constant - solids/liquids not calculated for K/Q -> won't affect equation
Determine Keq when... - reverse reaction: negative Kc - multiply rxn by constant: multiply Kc by factor - Adding multiple rxns: Qoverall = Q1 x Q2 x Q3 VS Koverall = K1 x K2 x K3
compare Q & K, what direction will it proceed in? - Q < K -> need to make more product, go right - Q > K -> need to make more reactant, go left - Q = K -> rxn at equilibrium
concentration vs pressure values for K or Q - Kp = Kc(RT)^ (change number gas moles) - Kc = values in concentration, mol/L - Kp = values in pressure, atm or Pa
Le Chatelier's principle - chem system at equilibrium disturbs -> reattains equation by undergoing a net rxn that decreases effect of disturbance
Concentration changes (le chateliers principle) - - concentration change: direction changes to re-establish original rations, no effect on K - Volume decrease by 1/2 -> conc. increase by 2 - Volume increase -> pressure becomes lower -> total number of gas molecules increase
pressure changes (le chateliers principle) - pressure change: change to reestablish original P ration, no effect on K (only for gases) - Increase: shift to side with less gas moles - Decrease: shift to side with larger gas moles
[A] -> B + heat - endothermic - temp increases because system absorbs heat by decomposing B -> increase Kc
[A] <- B + heat = endothermic - temp increases because system absorbs heat by decomposing B -> increase Kc
catalyst - non direction change/effect on K - rate forward increase -> reverse rate increase - get to same place faster
calculate new value of K at different temps ln(k2/k1) = (-∆Hrxn/r)*)(1/T2 - 1/T1)
Created by: ccottrel