Nitrogen and sulfur

Conditions and reasons for the Contact process

• Sulfur (or a sulfite ore) is burnt in oxygen to form SO2

• Reversible reaction of SO2 and O2 to form SO3 - conditions: 400-500*C (compromise - low to favour products side but high to ensure high rate of reaction), V205 catalyst (so that equilibrium is reached faster), 1-2 atm (high pressure favours products, but higher pressure than this is too expensive and would not increase the yield significantly), 1:1 ratio of reactants (this means oxygen is in excess, which shifts the p.o.e. to favour the products side of the reaction)

• Conversion of sulfur trioxide to sulfuric acid

Conditions and explanations for the Haber process

• N to H in a 1:3 ratio - this is the stoichiometric ratio in the equation

• 400-450*C temp - compromise between low temp needed to favour the forwards reaction, but high temp needed for a high rate of reaction

• 200atm pressure - high to favour the forwards reaction, but cannot be higher as it is too expensive to maintain, and equipment would have to be much stronger to minimise risk of explosion

• Iron catalyst so that equilibrium is reached faster

Formation of nitrogen oxides

Lightning, and in car engines

Removal of nitrogen oxides

Using a catalytic converter (a heterogenous catalyst) - platinum, honeycomb structure, also removes carbon monoxide and unburnt hydrocarbons

Formation of acid rain

• Nitrogen monoxide reacts with oxygen in the atmosphere to form nitrogen dioxide, which reacts with oxygen and water in the atmosphere to form nitric acid

• Nitrogen dioxide acts as a catalyst, oxidising sulfur dioxide into sulfur trioxide (nitrogen monoxide is formed, and the cycle continues), which reacts with rainwater to form sulfuric acid

Formation of PAN

Nitrogen oxides react with unburnt hydrocarbons to form PAN

Why is PAN a problem

It forms photochemical smog, which is dangerous to health