Dissociation of Water

Diana Gonzalez

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2H2O (g) ⇌ 2H2 (g) + O2

Pros and Cons of Water Dissociation

Pros:
  • Used to determine pH scale (more acidic or basic)
  • Water is a very versatile solvent because it forms hydrogen bonds with charged and polar covalent molecules
  • Water moderates temperatures on Earth
    - absorbs heat from warmer air and releases heat to cooler air


Cons:

  • H+ and OH- are highly reactive & can drastically affect chemistry of cell
    - Organisms are sensitive to changes in pH
  • If you add to many H+, water becomes acidic thus causing acid precipitation
    - pH of 5.6 and up
    - Acid precipitation washes away key soil buffers and nutrients (Ca/Mg)
    - A.P can increase concentrations of compounds to toxic levels (aluminum)

Chemical Shifts

According to Le Chatelier's Principle, if you make a change to the conditions of a reaction in dynamic equilibrium, the position of equilibrium moves to counter the change you've made.


Increase in temperature:

If you increase the temperature of the water, equilibrium will move to lower the temperature again by absorbing excess heat.

The forward reaction will be favored and more H+ and OH- will be made

----------------->

2H2O (g) ⇌ 2H2 (g) + O2


Increase in pressure:

If you increase the pressure in this reaction, the reaction will shift to the side with the least amount of moles, In this case, it will shift to the right since there are 3 moles on the right and 2 on the left. Similar to an increase in temperature, more H+ and OH- will be made


----------------->

2H2O (g) ⇌ 2H2 (g) + O2


Increase in concentration:

If you increase the concentration of H+, the reaction becomes acidic and OH- concentration decreases. Thus, the reaction shifts to the left in order to counteract the addition of H+

<-----------

2H2O (g) ⇌ 2H2 (g) + O2

Dissociation of Water Podcast