MOD 5

Question 1

What is a dynamic equilibrium?

Answer 1

A dynamic process in which a reversible reaction takes place in a closed system
The rates of forward and reverse reactions are equal and non-zero.
The concentrations of reactants and products will remain constant, but not necessarily equal
The macroscopic properties appear to be constant whilst the microscopic properties are in flux (movement)
(Macroscopic properties: colour, concentration)

Question 1

What is an example of a dynamic equilibrium?

Answer 1

A saturated solution is the simplest form of dynamic equilibrium to exist; any solute added after the solution has been saturated will form a precipitate. Whilst macroscopically the solution appears to be in a constant state, microscopically it is in fact in flux, as ions in the precipitate are continually dissolving into the solution whilst those in the solution are re-crystallising into the precipitate.

Question 2

What is a static equilibrium?

Answer 2

In contrast to a dynamic equilibrium where the rates of forward and reverse reaction are non-zero, The rates of forward and reverse reaction in a static equilibrium are zero.

Question 3

What is an example of a static equilibrium?

Answer 3

A common example is the conversion and interconversion of graphite to diamond
Graphite is converted to diamond under intense temperatures and pressures over millions of years, and the activation energy required for this to occur is thus very high, similarly, the activation energy required for the reverse reaction to occur is also very high.
The rates of forward and reverse reactions are ZERO. The forward and reverse reactions are NOT occurring.
As the activation energy of the reverse reaction increases, the percentage of particles that can collide successfully decreases
At very high activation energy (for reverse rn) values this proportion of particles tends to be zero, hence this reaction tends not to be reversible. We call this static equilibrium.

Question 4

Describe the dissolution process of ionic compounds

Answer 4

​​The Dissolution of ionic substances has 3 distinct steps:
1. The Breakdown of lattice-lattice (ionic) bonds
Requires an input of energy (endothermic)
2. Overcoming intermolecular interactions between water molecules (hydrogen bonds)
Requires an input of energy (endothermic)
3. The formation of ion-dipole interactions in hydration spheres
Releases energy (exothermic)

Question 5

How do ATSI people utilise solubility principles in detoxifying cycad?

Answer 5

ATSI people remove toxins from the cycad fruit using solubility equilibria principles. Cycads contain cycasin which is a toxin. The following processes are undertaken to detoxify cycad fruit:
- The seed is crushed to remove the outer shell and expose the inner seed
- Crushing increases the SA of the seed, which increases the rate at which the toxin is removed as per collision theory
- As cycasin is soluble in water, we can leech the seed of its toxin by using water to dissolve cycasin out of the seed.
Toxin in fruit (s) ⇌ toxins in water (aq)
However, as it is opened in an open system, the reaction could never reach equilibrium but the toxin could be successfully leeched due to its solubility.