From the simple processes of dissolution and crystallization in a saturated sugar solution to a complicated industrial process of oxidation and reduction in industry chemical equilibrium plays a major role.
Chemical equilibrium is the balance in the rate of two opposing reversible reactions with no change applied to the system with applied constant pressure and temperature. In a system where carbon monoxide is reacting with oxygen gas to form carbon dioxide there will be quantity of carbon monoxide left in the solution for as long as the reaction is placed. This is due to this reaction being a reversible reaction, although carbon monoxide and oxygen gas are synthesizing to form carbon dioxide, a contradicting reversible reaction is taking place, the decomposition of carbon dioxide to form carbon monoxide and oxygen gas.
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Figure 1: Chemical EquilibriumAs shown in Figure 1, in a reversible process, the rate of reaction for products turning into reactants [forward reaction] slows down as more reactants are changed into products simultaneously the rate of reaction of products changing into reactants [backwards reaction] speeds up. At a certain time for a specific temperature and pressure, the rate of reaction for both would be equal with no further change in the system.reaction-rate-time-graph.gif
Still, when the system is under influence of a change in temperature or pressure the reversible reaction would be affected. Le Chatelier’s principle generalizes this in “if a system in equilibrium is subjected to a stress the equilibrium will shift in the direction which tends to relive the stress”. (Le Chatelier’s Principle)
If the system is under the influence of a temperature altering the system will oppose this change. If an increase in temperature causes the increase in the rate of an endothermic reaction then the system will oppose this reaction by lowering the temperature thus favoring the endothermic reaction. Similarly, if the decrease in temperature increases the rate of the endothermic reaction, then the system opposes this stress by favoring the exothermic reaction.
Pressure, is another variable contributing in affecting the state of equilibrium that affects gaseous reaction only. If an increase in pressure is applied, then the system opposes this change by aiming to lower the pressure favoring the side with less gas molecules. Likewise, if a decrease in pressure is applied then the system opposes this change by increasing the pressure favoring the side with more gaseous molecules.
Several process in industry depend on Le Chatelier’s principle, the Haber-Posch process, the contact process, and the Ostwald process.
In the Haber process nitrogen gas from air reacts with hydrogen gas from natural gas [mainly methane] in order to provide ammonia gas. Since ammonia is a crucial substance in agriculture for the manufacturing of fertilizers it is vital to produce as much as possible in the lowest time possible.
N2(g) + 3 H2(g) is in equilibrium with 2 NH3(g) ΔH=-92KJ mol-1
The previous equation shows the chemical equation for the formation of ammonia. In order to obtain the highest amount of ammonia the reaction needs to be stimulated forward.
An increase in pressure would influence the system. By increasing the pressure, the system will oppose this stress by decreasing the pressure favoring the side with less gas molecules thus the forward reaction providing more ammonia gas. The process takes place in a pressure of 200 atm.
Since enthalpy of reaction is negative, then the forward reaction is an exothermic reaction. To induce the system into manufacturing further ammonia gas the temperature needs to be lowered. Yet, the low temperature would cause fewer collisions between particles causing the process to take more time. A compromise is put into action. The temperature is increased to 400-450ËšC with adding an iron catalyst. The iron catalyst works on lowering the activation energy needed for the reaction to occur thus ensuring that reaction takes time in as short time period as possible. (Clark,1)
Nitrogen gas is easily liquefied under high pressures and is collected separating it from nitrogen and hydrogen gas which are recycled.
Similar to the Haber Process, the contact process is an exothermic reaction in which sulphur dioxide gas is oxidized to produce sulphur trioxide, an initial step into forming sulphuric acid. (Clark,1)
2 SO2(g) + O2(g) is in equilibrium with2 SO3(g) ΔH=-197KJ mol-1
In this process also, a high temperature of around 400-450ËšC is used with vanadium pentaoxide catalyst and a high pressure of 100-200kPa.
In addition, the Ostwald process is in which nitric acid is formed in several steps; the oxidation of ammonia is a highly exothermic reaction which takes place in it. (Clark,1)
4 NH3(g) + 5 O2(g) is in equilibrium with4 NO2(g) + 6 H2O(g) Δ=-950KJ mol-1
To insure the highest possible amount of nitrogen dioxide formed a high pressure is used, with a great temperature of 900ËšC and a platinum-rhodium catalyst. (Clark,1)
Although sufficient solutions to producing essential products were obtained, limitations are found when considering the economic factor.
In the contact process, using a platinum catalyst would be more efficient but since it is highly expensive and susceptible to poisoning thus the platinum-rhodium catalyst is used. Moreover, high pressure is expensive to produce. First, extremely strong pipes and containment vessels need to be built to withstand such pressure, and the maintenance and running of high pressures are costly. (Clark,1)
Nitric acid is widely used in jewelry industry, when combined with hydrochloric acid it forms Aqua Regia, a reagent that is capable of dissolving important metals such as gold and platinum. It was often used in 1940 and 1965 as an oxidizer in liquid-propellant rocket engines. (Article Trader)
The Haber process has been identified as environmentally destructive. It abrupt the nitrogen cycle, pollutes ground water, and increases the levels of atmospheric nitrogen dioxide, a potential greenhouse gas. Yet, if it wasn’t for nitrogen fertilizers farmers wouldn’t be able to prosperous as much.
Sulphuric acid may show signs of harm and injury on plants reducing yield of certain crops, it may also dissolve in water droplets in clouds causing acid rain. It results in the damaging of wildlife and vegetation. Acid rain close to ground level can also cause damaging to building and statutes. On the other hand, sulphuric acid may reduce the invasion of pests or fungal diseases on plants causing plants to become healthier. Likewise, Nitric acid plays a major role in agriculture forming ammonium nitrate fertilizers. (Environment Agency)
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In the health factor, the excessive exposure to sulphur dioxide may harm the eyes lungs and throat. Furthermore, nitric acid is highly corrosive to the eyes, skin, and mucous membrane. (Environment Agency)Contact with dilute nitric acid concentrations may cause skin irritation, deep painful burns, and hardening of epidermis, while eye contact may cause severe burns and permanent damage. Inhalation of high concentrations may cause respiratory irritations with possible fatal effects. Ingestion of nitric acid results in the burning and corrosion of mouth, throat, and stomach. A dose of 10mL is fatal to humans. (Article Trader)
Science has proven to bring forth various solutions. Chemistry is no separate part of industry. It provides it with the most suitable and contemptible answers. Chemical equilibrium plays a major role in aiding to provide the utmost concentration of product needed. Several conflicts and damaging factors might be the result of such industrial processes but are all main reason behind erecting and the prosperity of the human society.
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