6.4- THE EQUILIBRIUM CONSTANT Kc Flashcards
What are homogeneous systems?
all reactants + products in same phase e.g. all liquids
What is produced when ethanol + ethanoic acid react?
ethyl ethanoate + water
If ethanol + ethanoic acid is mixed in a flask (stoppered to prevent evaporation) + left for several days with strong acid catalyst, what is obtained?
equilibrium mixture in which all four substances present
C2H5OH(l) + CH3CO2H(l) = CH3CO2C2H5(l) + H20(l)
How can the mixture of ethanol, ethanoic acid, ethyl ethanoate + water be analysed?
by titrating ethanoic acid with standard alkali (allowing for amount of acid catalyst added)
Why is it possible to titrate the ethanoic acid to analyse the ethanol, ethanoic acid, ethyl ethanoate + water mixture without significantly disturbing the equilibrium mixture?
as reversible reaction much slower than titration reaction
What does the titration of the ethanoic acid in ethanol, ethanoic acid, ethyl ethanoate + water allow us to work out?
allow us to work out number of moles of ethanoic acid in equilibrium mixture
What can you work out after the number of moles of ethanoic acid in the equilibrium has been worked out?
can calculate number of moles of other components (+ from this their conc. if the total vol of mixture unknown)
If several experiments are done with different quantities of starting materials, what is found to be constant?
C2H5OH(l) + CH3CO2H(l) = CH3CO2C2H5(l) + H20(l)
ratio of
[CH3CO2C2H5(l)]eqm [H20(l)]eqm / [CH3CO2H(l)]eqm [C2H5OH(l)]eqm
provided they’re done at same temp
What does the subscription ‘eqm’ mean in the constant value ratio?
concentrations have been measured when equilibrium has been reached
General expression that is constant, provided temp constant?
aA + bB + cC = xX + yY + zZ
[X]eqm^x [Y]eqm^y [Z]eqm^z / [A]eqm^a [B]eqm^b [C]eqm^c
What does the equilibrium constant change with?
temperature
What are the units of Kc like?
vary + must work them out for each reaction by cancelling out units of each term
