Wednesday, August 9, 2017

Geog notes + how buffer systems work

Geography notes

Basic rundown:

first, look at this structure of the earth(the width of the crust has been greatly exaggerated)
Heat from the core causes convection currents within the fluid mantle; the lower part of the mantle nearer to the core, upon heating, expands, decreases in density and rises. Thence, the heated mantle material, moving away from the heat source(core), cools down, and it contracts and sinks, causing movement. This process is known as convection, and it can happen within any fluid. The convection within the earth causes plates right above the site of convection to shift away from each other. If you visualize the entire process in a dynamic 3D model, then you can roughly see the powers of plate tectonics.

Movement of the plates can cause the otherwise stationary rock to be put under compressive stress. When the rocks slip, akin to the snap of a mousetrap, energy is released in the form of waves, and are known as earthquakes.

There are 4 types of earthquakes;

- Longitudinal waves
- Sinusoidal waves
- Rayleigh waves
- Love waves

Sinusoidal waves, being as they are, are much more destructive, but slower, than longitudinal ones. Longitudinal waves are faster but less destructive. In certain towns, people position longitudinal sensors around the area. That way, the longitudinal, being less deadly, can strike first and people have time to evacuate when the sinusoidal wave comes.

Volcanoes 

Structures of volcanoes are as such: boiling pots of magma known as magma chambers expose magma within to high pressures and temperatures, and travel up through cracks in the earth's crust. Sometimes they enter the surface and cool down, over time forming elevated scopes of land known as volcanoes. Even among volcanoes, there are different types of lava, depending on their viscosity(cite physics here). Stickier, more viscous magma tends to build within itself more pressure and have the more explosive eruptions.

Runnier, less viscous lava tend to have less BOOM eruptions.

Ash, pyroclasts, and gases are ejected during eruptions, they can be hurled into the atmosphere, exist in pyroclastic flow or pyroclastic surges. A few case studies:

Krakatoa

Indonesian volcano, a blast so loud that even residents in Singapore heard its BOOM!

Eyjafjathalökull

The eruption caused the ash to block flight paths. Should such an eruption happen in Singapore, even for a few weeks, billions of dollars could be lost.

Mt. Pelee

Apparently one of the two people who survived this devastating eruption was only because he was in solitary confinement :l.


How Buffers work
Le Chatelier’s principle


Le Chatelier’s system concerns itself with the forward and reverse chemical reactions, denoted with ⇋. Assume we have a system of A + B  ⇋ C + D, and assume they are in equilibrium.

By equilibrium, it means that the rate of forward reactions, that is, A and B combining to form C and D, is equal to rate to the backward reactions, C and D to form A and B.

There are 3 cases of changing this system of equilibrium.

Adding more reactants:
An increase in reactants of A or B or both would generally result in an increase in C and D, and also C and D back into A and B. You are essentially having the same reaction but on a larger scale. If we added A or B singularly, C and D would increase, but the other reactant that wasn’t added, due to increased, a higher rate of forward reaction, would decrease. In Haber process, we use extra Hydrogen because Nitrogen is harder to get, and this maximizes the use of Nitrogen gas in the process.

Less of A or B would result in Forward reaction lessening, and backward remains the same, favoring backward reaction.

Adding heat:

First and foremost, do accept the concept of heat having an increased rate of particles colliding with each other as its discrete phenomena with its own consequences, irrespective of the phenomenon I will explain.

In the Haber process, the forward is exothermic, and the backward is endothermic. Both parcels of information are equally important, as you will see soon. Adding heat to the Haber reaction would result in the Ammonia gas having a higher chance and rate to grab this excess heat in a disordered system of molecular collisions and revert back into Nitrogen and Hydrogen gas. The rate of NH3 absorbing heat and turning back into reactants is increased and greater than the forward reaction.

Simultaneously, the reaction to reach equilibrium is faster due to the higher rate of reaction, the Haber process utilises this sweet spot of (how many ºcelsius again?)

Adding pressure:

The forward reaction to combine the two gases into one gas is favored because it increases the rate of the more abundant Nitrogen and Hydrogen gas into ammonia, while the rate of backwards reaction is constant.


Conjugate acid-base pair.

First and foremost, review Brønsed Lowry’s definition of acid and base(Keep in mind the definition only applies in the context of conjugate acid-base pairs): An acid refers to a substance that has the ability to donate a H+ Ion and a base is one that can accept such an ion. They are a subset of reversible reactions which includes the exchange of H+ ions.

This differs from our definition of a base; a base is one that dissociates to form OH- Ions. The OH- ions are the base here, and the substance that dissociates to form them, in our standard definition, are bases.

With this more general definition of an acid and base, we can give an example of a conjugate acid-base reaction.

HCl + H2O ⇌ H3O+ + Cl-

Cl-, while not a base, accepts a hydrogen plus ion in the backward reaction. It is, therefore, a base(in this context), and HCl an acid; they are a conjugate acid-base pair. Hydronium and water is the other pair.

Application of conjugate acid-bases:

They are used in buffers(solutions that resist PH changes)

Take this system in blood,

CO2(g) + H2O(l) ⇋ H2CO3(aq) ⇋ HCO3-(aq) + H+(aq)

Remember that the H2CO3 is not completely aqueous; it only partially ionizes to form 2H+ and CO32-

Carbon Dioxide is defined as acidic because it reacts with water to produce carbonic acid.
Having more Carbonic acid is generally better than having lots of dissociated bicarbonate ions and H plus ions.

Our body uses buffers too! When we hold our breath, CO2 that is turned into carbonic acid is accumulated in our blood. Acidosis refers to excessive acids(carbonic acid) in our tissues, most commonly lungs. We breathe out CO2, which is acidic, and in turn, H2CO3 decomposes into bicarbonate and H+ ions, and our kidneys release these H+ ions in the form of urine. The reason why urine become more acidic and smelly when we do not drink enough water is that there is more water to dilute Carbonic acid in our urine, and secretes Bicarbonate into the blood.

On the contrary, Alkalosis is managed by withholding urine and the lungs do not secrete as much CO2.

Now, applying Le Chatelier’s principle:

The blood, on top of the above system, also has a self-governing, autopilot system to maintain a PH. a greater concentration of H+ ions would result in a greater rate of  H2CO3(aq) ⇋ HCO3-(aq) + H+ (backward), minimizing the effect of H+ concentration. Excess HCO3- does the same thing!

A more general theory of buffer systems

Buffer systems work on reversible reactions, made understood by Le Chatelier’s principle. They dampen, but not totally prevent, the addition of extra hydrogen ions or basic ions. In a more specific context,
(Let B be a base)
HnB ⇋ B-n + nH+

Moved by the concepts of Le Chatelier's principle buffers are made thus. 

Looking at water in a new perspective

H3O+ + OH- ⇋ 2H2O
Protonation refers to giving away a proton, aka H+ ion. Deprotonation is vice versa. It is an example of Autoprotolysis, aka auto(being itself) receives a transfer in protons.

The reason we know these reactions have occurred is that water has an electrical conductivity(most everything does, but the fact that they do tells me that there ARE ions)

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