equilbrium and redox (1 Viewer)

[dgt20]

was wondering if someone could give me some simple basic notes on equilibrium and redox reactions for next year, if not notes just some basic introduction on important terms. thanks

 

[captainhelium]

Hmm..I just finished my HSC Chemistry exam at the end of last month so I'll see what I can remember to help you out. I'll go over redox reactions first since they're covered in Production of Materials (which is the first module). I hand-wrote my notes instead of typing them so unfortunately I can't send you digital copies of my stuff but I will try to summarise the main concepts for you.

REDOX REACTIONS

• Redox reactions involves a transfer of electrons between two chemical species
• Redox reactions consist of an oxidation reaction and a reduction reaction. One of the chemical species undergoes oxidation and the other undergoes reduction. Together, this forms a redox reaction.
• Oxidation is the loss of electrons of a particular chemical species and reduction is the gain of electrons of a particular chemical species. The species undergoing reduction gains the electrons that were lost from the species that was oxidised. I know this sounds confusing and might be tough to remember that oxidation involves a loss of electrons and that reduction involves a gain of electrons. In school, I used an acronym called OILRIG which basically meant that: Oxidation-Is-Loss-Reduction-Is-Gain
• For example, consider a situation where a zinc metal plate is dipped in a solution of silver nitrate. The zinc metal plate oxidises and loses electrons. These electrons are then gained by the silver nitrate solution which hence reduces (since reduction is gain). Essentially, this results in copper losing electrons and silver ions from the silver nitrate gaining electrons. The reactions involved are:
  - --> OXIDATION
  - + --> REDUCTION
• So how do you tell what oxidises and what reduces? In the Production of Materials module, the species that oxidises is the more reactive metal (this is a simplification however). In this case, copper is more reactive than silver and so copper oxidises and loses electrons. As a result, the silver ions are reduced and gain these electrons from the copper as it is less reactive.
• Now in terms of product, we should see that in the above equations that Copper ions are formed () and that solid silver is formed.
• These redox reactions often occur in a galvanic cell. An example of a galvanic cell containing copper and silver can be seen through this link.
• Basically, the copper plate loses electrons as it oxidises and these electrons travel towards the silver solution on the other side through a wire. The silver ions in the solution 'use up' these electrons and become silver solid (from the reduction equation). As a result, 'extra silver' is being deposited on the silver plate seen in the diagram in the link.
• Also, due to oxidation of copper, there are extra copper ions being released in the copper solution in the diagram and so the blue intensity of the copper solution would increase.

Yeah idk if that made sense or not - it's kinda hard to explain without diagrams and actually thinking down and writing carefully instead of just writing what's in my head. Anyways, for equilibrium,

EQUILIBRIUM
Essentially, its a reaction in which the forward and reverse reaction occur at the same rate. A common equilibrium reaction is the dissolution of carbon dioxide in water which is also a common exam question:
- carbon dioxide gas + water ⇄ carbonic acid (this equation is a simplification however)

What's important to note about equilibrium reactions is something called Le Chatelier's Principle. Essentially it states that when an equilibrium is disturbed, the system will respond to minimise the disturbance. In the HSC Course, equilibrium's can be disturbed by changes in concentration, temperature or pressure.

For example, let's consider the carbon dioxide equilibrium. The forward reaction is exothermic (meaning that carbon dioxide and water becoming carbonic acid releases heat). Say we DECREASE the temperature of the system (e.g. by putting it in a fridge or something)- this means that the system will naturally try to oppose this change by INCREASING the temperature by Le Chatelier's principle. As a result, the forward reaction will be favoured since it is exothermic (producing heat).

What this results in is that the equilibrium shifts to the right to produce more carbonic acid as this is an exothermic reaction (thus minimising the change that we made). Thus, from decreasing the temperature, carbon dioxide solubility is increased since carbonic acid is aqueous.

Eek, idk if I explained that well enough. I kind of rushed doing this but if you need more help let me know! It's a bit hard to explain without diagrams and stuff but I hope it helps to some extent.

Good luck for Chemistry!