Equilibrium Flashcards
Kc formula
[Product]^no of moles / [reactant]^no mols
Kc is constant providing
Temp is constant, products and reactants in same phase.
High Kc means
Goes to completion
Low Kc means
Reaction does not happen
Kc = 1 means
Comparable amount of reactants and products
What happens if increase conc.
Kc constant independent of conc. so conc of increased decreases and conc. unchanged increases
What happens if increase pressure
Kc constant independent of pressure so mols of increased decreases and mols unchanged increases
What happens to Kc if temp increase
Kc increase if enthalpy of reaction positive, otherwise decrease
What happens to Kc if temp decrease
Kc increase if enthalpy of reaction negative, otherwise decrease
How to calculate partial pressure
mol/total mols * total pressure
Kp formula
PP of product^mols/PP of reactants^mols
Heterogenous Kc
Conc. of pure solid/liquid taken to be 1 (because it is constant)
Bronsted-Lowry definition of acid
Proton donor
Bronsted-Lowry definition pf base
Proton acceptor
Formula for pH
-log([H+])
Kw
1 * 10^-14
Ka formula for acid HA
= ([H+}[A-])/[HA]
Strong acid Ka value
Very high,»_space;1
Weak acid Ka value
Very small «1
Formula for finding pH of weak acid
Ka = [H+]^2 / [HA]
pH curve of adding 0.1M 25cm-3 strong base to 0.1M 25 strong acid
Initial pH 1, Equivalence point at 25 where pH goes from 3 to 11, middle of this jump is 7. Asymptotic to 13
pH curve, weak acid titrated with strong base
Starts at 3, buffer region until just before 7, pH equivalence at >7. Jump from 7 to 11. Asymptotic to 13.
pH curve, strong base with strong acid
opposite of strong acid with strong base
pH curve, weak base with strong acid
opposite of weak acid with strong base
Finding pKa from titration line
Assume that weak acid has not dissociated in solution without base.
At half neutralisation (added 12.5), [HA] = [A-], therefore using Ka formula, they cancel and Ka = [H+]. So pKa = pH at half equivalence
Diprotic acid pH curve
When adding strong base to weak acid, 2 equivalence points, one from >1 to 4, one to 5 to 11.
How does an indicator work
HIn H+ + In-
HIn is a different colour to In-. Conc of H+ affects equilibrium
Equivalence point
Same number of mols of acid and base
End point
When indicator changes
What makes successful indicator
End point = equivalence point
Colour change should be within pH jump for sharp colour change over 1 drop
Diluting strong acid by 10 does what to pH
Decreases by 1
Diluting weak acid by 10 does what to pH
Decreases by 0.5
