⋆˚࿔✮⋆˙Making Science Fun! (2nd Entry)

Topic: Equilibria

⋆｡˚⭒°✮˙⋆Important Definitions⋆˙✮°⭒˚｡⋆

• Acid - Proton Donor.
• Base - Proton Acceptor.
• Reversible Reaction - A reaction that does not go to completion and is represented by a reversible arrow.
•  Equilibrium - The point in a Reversible reaction in a closed system where the rate of forward reaction is equal to the rate of backward reaction.
• Dynamic Equilibrium - The point in a reversible reaction in a closed system where the rate of forward reaction is equal to the rate of backward reaction, and the amount of reactants and products remains constant.
• Exothermic - A reaction in which energy is released into the surroundings, and enthalpy change is negative.
• Endothermic - A reaction in which energy is absorbed from the surroundings, and enthalpy change is positive.

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Le Chatelier's Principle

The principle states that if a system at Equilibrium is disturbed by changing conditions, the position of equilibrium will shift so as to counteract the change, and a new equilibrium is established. 

Factors affecting the position of equilibrium

1.  Changes in Temperature: Depends on if forward and backward reaction is exothermic or endothermic
2. Changes in Pressure: Only affects gaseous reactions. Pressure of a gas ∝ number of moles 
3. Changes in Concentration

*Note: Adding a catalyst has no effect on position of equilibrium, only on the rate of reaction 

 Examples of Reactions using Dynamic Equilibrium in Chemical Industry

✮⋆The Haber Process  ⋆˙✮°

This process is for the Industrial Manufacture of Ammonia

N2 + 3H2 ⇌ 2NH3    ΔH = -94kJ

Conditions

• Temperature: 450˚C
• Pressure: 200~250 Atm
• Catalyst: Finely divided iron

°✮⋆The Contact Process  ⋆˙✮°

This process is for the Industrial Manufacture of Sulphuric Acid

S+ O2 ⇌ SO2

2SO2 + O2 ⇌ 2SO3

Conditions

• Temperature: 450˚C
• Pressure: 2 Atm
• Catalyst: Vanadium IV Oxide (V2O5)

SO3 + H2O → H2SO4

SO3+ H2SO4 → H2S2O7

H2S2O7 + H2O → 2H2SO4

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The Brønsted-Lowry Theory

When an acid reacts with a base it donates a proton and the base accepts it, and the acid forms it’s Conjugate-Base and the base forms a Conjugate-Acid. 

Conjugate Acid - A species formed by association with a proton

Conjugate Base - A species formed by the loss of a proton

✮ Some common acids are Hydrochloric Acid (HCL), Sulfuric Acid (H2SO4), Nitric Acid (HNO3), Ethanoic Acid (CH3COOH)

✮ Some common alkalis are Sodium Hydroxide (NaOH), Potassium Hydroxide (KOH), Ammonia (NH3)

pH and the pH scale

The pH gives a measure of the concentration of H+ ions in solution. It is defined more appropriately as 'The logarithm to the base of the reciprocal of the hydrogen ion concentration'. 

It sounds complicated, but it's really just describing the equation shown below: 

       pH =  log₁₀  ( ⅟ [ H⁺ ])

pH = - log10  [ H + ]

[ H + ] = 10--pH

*  [  ] = concentration in mol per dm3

 ✮˙⋆  The pH scale ⋆˙✮°

     [ H + ] > [ OH -- ]                                 [ H + ] = [ OH -- ]                                 [ H + ] < [ OH -- ]