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Acids, bases and chemical equilibrium: Kw, Kc, Le Chatelier
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- 1Identify and deduce the formula of the conjugate acid of any Bronsty-Lowry base 1. NH3 2. CH3COO- 3. HPO4(2-)1. NH4+
2. CH3CHOOH
3. H2PO4(-) - 2Identify amphiprotic species that can act as Bronsty-Lowry acids and baseH20, HC03, H2PO4, HSO4
- 3Formula for [OH-][OH-] = 10^-pOH
- 4Formula for [H+][H+] = 10^-pH
- 5What is constant of water?Kw=1.00 x 10^-14
(Kw = [H+][OH-] - 6Distinguish between strong and weak acids and bases in terms of the extent of dissociationEOD
- SA: Completely dissociates into ions in aqueous solution (higher Ka)
- WA: Partially dissociates into ions (lower Ka value)
- SB: accepts protons easily (high Kb value)
- WB: Partially dissociates into ions (lower Kb value) - 7Distinguish between strong and weak acids and bases in terms of the reaction with waterSA: will fully ionise/ dissociate producing H3O+ ions from water
WA: partially ionise, leaving some unreacted acid remaining
SB: Fully accepts protons and so produces OH- ions from water
WB: Will partially accept protons from water to form conjugate acid - 8Distinguish between strong and weak acids and bases in terms of the electrical conductivitySA: More effective electrical conductor as more ions dissociated in solution
WA: Less effective electrical conductor as less ions dissociated in solution
SB: More effective electrical conductor
WB: Less effective electrical conductor - 9What does polyprotic and monoprotic mean?acids that act as proton donors can be classified as monoprotic and polyprotic depending on the number of protons donated
- 10Expression for Kc[products]^coefficients/[reactants]^
coefficients - 11Deduce the extent of reaction from the magnitude of Kc constant. a) Between 10^-4 and 10^4 b) >10^4 c) <10^-4a) Extent of reaction is significant. Appreciable concentrations of both reactants and products are present at equilibrium
b) Almost complete reaction occurs. The concentrations of products are higher than reactants at equilibrium
c) Negligible reaction occurs. The concentrations of reactants are considerably higher than products - 12Using Le Chatliers Principle, predict effect of added reactant on position of equilibrium and value of KcIf H2 is added to to equilibrium system, the system will shift to decrease the concentration of the added N2, so a net forward reaction occurs.
- 13Using Le Chatliers Principle, predict effect of increase pressure on position of equilibrium and value of KcPosition of equilibrium will move in the direction of the fewest gas particles. An increase in pressure will cause a net forward reaction to occur in order to reduce the overall pressure.
- 14Using Le Chatliers Principle, predict effect of dilution on position of equilibrium and value of KcShift in the position of equilibrium towards the side that produces a greater number of dissolved particles. A net reverse reaction will occur, increasing the total no. of particles in solution.
- 15Using Le Chatliers Principle, predict effect of increasing temperature on position of equilibrium and value of KcExothermic reaction: reaction that can 'oppose' an increase in energy by absorbing energy. As reverse reaction is endothermic, this favours a net reverse reaction.
- 16Using Le Chatliers Principle, predict effect of catalyst on position of equilibrium and value of KcCatalyst lowers the activation energy of the forward and reverse reaction by the same amount. The lower activation energy causes an increase in the number of effective collisions; increases rate of forward and reverse reaction equally. *It doesn't change POE, only how quickly E is attained.
- 17Explain effect of adding reactant using collision theory and reaction rateBecause concentration of N2 has increased, the rate of forward reaction initially becomes greater than the rate of reverse reaction. Thus, as the concentration of N2 and H2 decreases and concentration of NH3 increases, the rate of forward reaction decreases and the rate of reverse reaction increases, until they become equal again.
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