Haber process
- Ammonia is manufactured from nitrogen and hydrogen through a revisable process called Haber process.
- The nitrogen and hydrogen must be pure.
- 1 mole of nitrogen is reacted with 3 moles of hydrogen.
- N2 (g) + 3 H2 (g) 2 NH3 (g) (ΔH = −92.4 kJ•mol−1)
- This is done at 200 atmospheres and between 300 and 550 °C, passing the gases over four beds of catalyst, with cooling between each pass to maintain a reasonable equilibrium constant. On each pass only about 15% conversions occurs, but any unreacted gases are recycled, so that eventually an overall conversion of 98% can be achieved.
Contact process
- Is used to produced Sulphuric acid
- The first step to is preparation and purification of sulfur dioxide
- Catalytic oxidation (using vanadium pentoxide catalyst) of sulfur dioxide to sulfur trioxide
- Conversion of sulfur trioxide to sulfuric acid
- The average percentage yield of this reaction is around 30%.
H2S2O7 (l) + H2O (l) → 2 H2SO4 (l)
Reversible reaction
- A reversible reaction is a chemical reaction that results in an equilibrium mixture of reactants and products.
- The concentrations of reactants and products in an equilibrium mixture are determined by the analytical concentrations of the reagents and the equilibrium constant, K.
- when the free energy change is large (more than about 30 kJ mol-1), then the equilibrium constant is large (log K > 3) and the concentrations of the reactants at equilibrium are very small. Such a reaction is sometimes considered to be an irreversible reaction, although in reality small amounts of the reactants are still expected to be present in the reacting system.
- E.g. 2NaCl + CaCO3 → Na2CO3 + CaCl2 Na2CO3 + CaCl2→ 2NaCl + CaCO3
- This is an example of reversible reactions
- H2(g) + F2(g) ------> 2 HF(g) forward
- H2(g) + F2(g) <------ 2 HF(g) reverse
- Reversible chemical reactions follow a similar pattern. The reactants are initially the only molecules around. They react to form products. The amount of reactants dwindles and the forward reaction slows down. The product amounts increase at the same time the reactants are disappearing. They products "decompose" to form reactants. The rate for this reverse reaction increases as the amount of product grows. Ultimately there comes a time when the forward reaction rate and the reverse reaction rates are equal.
- At equilibrium the numbers of reactant and product molecules stays constant. The identity of individual molecules keeps changing.
by Poyu and Xavier
