Chemestry 3

Chemestry 3

1. Reaction at equilibrium

   • The products become in reactants and at contrary, this cyclical process in the same ratio, so there is not change in concentratation.
   • Constant K
     • To any specified temperature if we have  aA+bB<=>cABThenK=activity of products/activity of reactants This "activity" depends of the state of the susbtances. *Gas=Partial pressure divided over bar  *Solid or liquiud= 0 (zero) *Aqueous solution= Molarity The activity of aqueous solution can be interpreted as ions, (You write the ionic reaction, and from this you make the activities for each ion) REMEMBER THAT THIS IS A CONSTANT, SO THE UNITIES ARE CANCEL.
   • Kind of
     • Homogeneous equilibrium
       • All substances in the reaction have the same state
     • Heterogeneous equilibrium
       • When the substances in the reaction have diferent states

2. Free energy

   • The change of free energy of the reaction is zero when theaction is on equilibrium
   • Molar free energy
     • Δ Gm=RT*ln(M2/M1) Where Δ Gm= Change molar of free energy R=constant like 8.31451 J/(mol*K) T=Temperature M= Molarity one and two (the latest is the new (2), the other is the first (1)) 
   • Not equilibrium
     • Change in the reaction
       • Change of the free energy of the reaction ΔGr ΔGr=ΔGr°+RT*ln(Q) Where ΔGr°= Change of free energy of the reaction at STANDARD conditions R=Constant like 8.31451 J/(mol*K) T=Temperature Q=activities of products/activities of reactants Here applies too the condition about the state of the substance.
   • At equilibrium
     • IS ZERO

3. Constant K

   • ΔGr=0  Then  ΔGr°=-RT*ln(K) Generally here i have to get K, so they give the other variables.  It is important that  ΔGr°=a*ΔGf(products) - b*ΔGf(reactants) Gf=Free energy of formation a and b amount of moles of the reaction,
   • Constant Kc
     • Conversion K=(R*T)^(change n)*KcRemember that here R=0.0831451 bar*L/mol*k
   • Change in the reaction
     • *If you multiply the chemist reaction per a number, then the constant is elevated to this value. *If you change the order of the reaction, so pass the products to reactants and viceverse, the constant k will be 1/k in relation with the original
   • k is big or small
     • Big= More products Small=More reactants

4. direction of reaction

   • If  k>Q : From reactants to products k<Q: From products to reactants  Here, generally, they give k, and i look for Q.

5. Equilibrium composition

   • 1. Anote initial concentrations 2.change of concentration (the stoichiometryc coeffcient per x with sign negative if it is reactant and positive if it is product) 3.Replace this data (each new concentration) in equation of the constant (the problem gives this generallly). If k is small, like 10^-30 then i can simply the ecuation saying that x=0 for reactants That is all, just get x, (sometimes is a quadratic equation) and put it in the concentrations and you will have the answer. x has to be positive, and let the all the concentrations positives.
   • Percent descomposition
     • Amount that has been descompound. (precent in relation with the initial concentration)
   • If i add moles of
     • If i change the concentration of any substance of a equilibrium reaction, to calculate the new concentrations in the reaction to the new equilibrium: 1.Calculate the initial amount of moles of the substances that change concentration (from the concentration of the almost last equilibrium) and sum or rest the amount of moles that won or lost, You have the volume of mixture,  2. calculate the NEW CONCENTRATION, from that substances, from the new amount of moles and the volume of the solution.  3. Make exactly the same process to find x from K (it does not change), you let like initial concentrations, the originals, just replace that of that substance. the change of the concentration (stoichiometric coeffcient with x) will have a sign according with who will lose matter, reactants or products. 4.Find x and calculate the new mixture concentrations.
   • If increase temperature
     • First i get  ΔHr°=a*ΔHf(products)-b*ΔHf(reactants) ((It has the same structure of  ΔGr°)) If these enthalpy is positive the reaction is endothermic, if is negative the reaction is exothermic. If I INCREASE TEMPERATURE: *in an endothermic reaction favor products *in an exothermic reaction favor reactants