CHE 141 1st Edition Lecture 39Chemical Kinetics- For any reaction aA+bBcC+dD the relative reaction rate by: -1/a x delta[A]/delta t=-1/b x delta [B]/delta =1/c x delta [C]/delta t=1/d x delta[D]/delta t- For the reaction A+BC, the following generic rate law relating concentration of reactants and the experimentally determined rate of reaction is Rate=k[A]^m[B]^n- Overall reaction order m+n- For the first order reaction: ln[X]=-kt+ln[X]0- For second reaction: 1/[X]=kt+1/[X]0- Arrhenius equation: k=Ae^-Ea/RT- Linear form of Arrhenius equation: lnk=-Ea/R(1/T)+lnA- Plotting k against 1/T gives a straight line with gradient –Ea/R and intercept =lnA- Ea=-gradient x R- Molecularity describes the number of ions, atoms or molecules involved in an elementary step in a reaction- The rate determining step is the slowest elementary step in a chemical rection and the rate of this step controls the overall reaction rate- A catalyst is present at both the beginning and end of a reaction - An intermediate is not present at the beginning or end of a reaction-it is produed and then consumed during the reactionThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Chemical Equilibrium- At equilibrium Rateforward-Ratereverse- For aA+bB reversible cC+dD- Equilibrium constant expression is: Kc=[C]^c[D]^d/[A]^a[B]^b- K>>1 products>>reactants equilibrium lies to the right- K<<1 reactants>>products equilibrium lies to the left- Heterogeneous equilibria do not include (s), (l) or H2O (aq) in equilibrium constant expression- Relationship between Kp and Kc: Kp=Kc x (RT) delta n- For reverse reactions: Kforward=1/Kreverse- When an equation is multiplied by n: K2=K1^n- For combined reactions: Koverall=K1xK2xK3xK4…xKn- For a mass action expression we use the reaction quotient instead of K- Q<K forward direction- Q=K equilibrium- Q>K reverse direction- Le Chateliers Principle states that if a system at equilibrium is stressed, the position of equilibrium shifts in the direction that relieves that stress- Catalysts have no effect on equilibrium postionAqueous Equilibrium- Bronsted Lowry acid donates a proton(H+)- Bronsted Lowry base accepts a proton (H+)- A strong acid fully ionizes with Ka>>1 - Strong base fully ionizes with Kb>>1- P=-log- pH=-log[H3O+]- pOH=-log[OH-]- Kw=[H3O+][OH-]=1.00x10^-14- pKw=pH+pOH=14- weak acids: Ka=[H3O+][A-]/[HA]- weak base: Kb=[HB+][OH-]/[B]- Acid base properties of anions:o An anion that is the conjugate base of a weak acid is itself a weak baseo An anion that is the conjugate base of a strong acid is pH-neutral- Acid base properties of cationso A cation that is the counterion of a strong base is pH neutralo A cation that is the conjugate acid of a weak base is a weak acido A cation that is small and highly charged metal is a weak acid- Neutral salts: salts in which neither the cation nor the anion acts as an acid or a baseo Cation=counterion of strong baseo Anion=conjugate base of strong acid- Basic salts: salts in which the cation does not act as an acid and the anion acts as abaseo Cation=counterion of a strong baseo Anion=conjugate base of weak acid- Acidic salt: salts in which the cation acts as an acid and the base does not act as a baseo Cation=conjugate acid of weak base or small, highly charged metal iono Anion=conjugate base of strong acid- Common ion effect: the shift in the position of an equilibrium caused by the addition of an ion taking part in the reaction. If there is a common ion then its initial concentration in the ICE table is not zero- A buffer solution resists changes in pH when acids or bases are added to it; thus they must contain a weak conjugate acid-base pair- Henderson-Hasselbalch: pH=pKa+log [base]/[acid]- Buffer range=pKa
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