19.1 - The Equilibrium Constant Kc Flashcards
What does the unit of Kc depend on
The number of concentration terms on the top and bottom of the equilibrium constant term
How do you calculate the units for kc
Using the kc equation, insert the unit moldm^-3 and calculate accordingly
What two main types are equilibria
Homogenous
Heterogenous
A homogenous equilibrium contains…
…equilibrium species that ALL have the same state or phase.
A heterogeneous equilibrium contains…
…equilibrium species that have different states or phases.
In _____1_____ equilibria, the Kc expression contains concentrations of all species. However, in _____2_____ equilibria, the concentration of solids and liquids are essentially constant. So any species that are solids and liquids are _____3_____ from the Kc expression.
- Homogenous
- Heterogenous
- Omitted
What to keep in mind when calculating Kc
Read questions carefully
Can only use equilibrium concentrations NOT initial so have to calculate from equation
Also use CONCENTRATIONS not moles so may need to divide by the volume
Determining Kc from experimental results
- In a conical flask, mix together 0.100 mol carboxylic acid (eg. CH3COOH) and 0.100 mol alcohol (eg. C2H5OH). Add 0.0500 mol HCl as an acid catalyst
TOTAL VOLUME OF MIXTURE IN FLASK IS 20.0cm^3
AMOUNT OF WATER IN ACID CATALYST IS 0.500 mol - Add 0.0500 mol HCl to a second conical flask as a control
- Stopper both flasks and leave for a week to reach equilibrium
- Carry out a titration on the equilibrium mixture using a standard solution of sodium hydroxide.
- Repeat the titration with the control to determine the amount of acid catalyst that has been added
Determining Kc from experimental results
RESULTS
By analysing the two titration
Amount of HCl(aq) in the control = 0.0500 mol
Amount of acid (HCl and CH3COOH) in equilibrium mixture = 0.115 mol
