Equilibria Flashcards
Dynamic Equilibrium
In a closed system a reversible reaction will reach a state of dynamic equilibrium where the forward and backward reactions are taking place at exactly the same rate.
Le Chatalier’s Principle
When a reversible reaction is in equilibrium and you make a change then the reaction will go in the direction to oppose the change.
Effect of Temperature
• Increasing temperature favours the endothermic direction, which leads to an increase in yield
• Decreasing temperature favours the exothermic direction, which leads to a decrease in yield
Effect of Pressure
• Increasing pressure shifts equilibrium in the direction that produces less moles/molecules of gas (increasing yield of side with fewer moles)
• Decreasing pressure shifts equilibrium in the direction that produces more moles/molecules of gas (increasing yield of side with more moles)
Effect of Catalyst
Increase the rate of both reactions equally (no change in yield or equilibrium point, just how fast equilibrium is reached)
Concentration of Reactants
• Increased conc or added reactants favour forward reaction and increase yield of products
• Decreased conc or remove some reactant favour backward reaction and decrease yield of products
The Haber Process Equation
N2 + 3H2 <> 2NH3
Haber Process General Info
- Method used to make ammonia gas in industry
- Nitrogen is extracted from air by fractional distillation
- Hydrogen is obtained from either cracking hydrocarbons or reacting methane and water
- Reversible reaction with conditions that aim to produce most ammonia possible
HP Condition: Temperature
- 450 degrees (moderate temperature)
- Forward reaction is exothermic (negative change in enthalpy) and is favoured at a low temp
- At too low temperatures the reaction is too slow (Coll. Theory)
- Compromise is made between yield and rate
HP Condition: Pressure
- 200 atm (HIGH pressure)
- High pressure favours side with fewer moles (right side), increases yield of ammonia
- Reaction rate also increases with pressure (Coll. Theory)
- Compromise to create safety and cost efficiency (pressure means higher risk of explosion and thicker walls are built for higher pressures)
HP Condition: Catalyst
- Iron catalyst
- Speeds up both reactions equally
- No effect on yield but product is obtained more quickly
HP Conditions: Other
1) Remove product as it’s formed : prevent ammonia from breaking down again
2) Recycling unreacted gases : gives nitrogen and hydrogen another chance to react at catalyst + improve yield
Uses of Ammonia
• Fertilisers
• Nitric Acid
• Explosives
• Dyes
• Medicines
Nitrogen in Fertliser
- Nitrogen is used to make proteins for growth, taken in at roots as mostly nitrates
- Made by neutralising nitric acid or sulphuric acid with ammonia solution
Potassium in Fertliser
- Helps protect plants against disease
- Example fertiliser: Potassium Nitrate
- Occurs naturally
Phosphorus in Fertiliser
- Improves crop yields and helps roots to grow and crops to ripen
- Example fertiliser: Ammonium Phosphate
- Made by neutralising phosphoric acid with ammonia solution
