chemistry - extracting metals and equilibria

• displacement reactions are redox reactions - Oxidation Is Loss of electrons Reduction Is Gain of electrons (OILRIG)
• the reactivity series of metals (potassium, sodium, calcium, magnesium, aluminum, (carbon), zinc, iron, (hydrogen), copper, silver, gold)
• most metals are extracted from ores found in the Earth’s crust. Unreactive metals are found in the Earth’s crust as the uncombined elements
• the extraction of metals involves reduction of ores - (reduction is gain of electrons/ loss of oxygen)
• Metals which are lower than carbon in the reactivity series can be extracted by heating with carbon. Metals higher than carbon in the reactivity series can only be extracted using electrolysis.
• Phytoextraction involves growing plants on ground that contains metal compounds. The plants absorb the metal compounds through their roots. The plants are then harvested and burned to form ash. The ash contains the metal compounds needed.
• Bacterial extraction involves using bacteria to extract metal compounds from rock. The bacteria live on the rock and produce a solution called leachate. The leachate contains the metal ions needed.
• Biological methods of metal extraction use less energy and are less polluting than traditional mining.
• Phytoextraction is a slow process. This is because plant roots only absorb metal compounds slowly.
• In bacterial extraction, the leachate produced can contain toxic substances.

  For example, it may contain sulfuric acid, which damages the environment
• In the reactivity series - the higher up a metal, the greater the tendency to form cations. the lower down a metal, the greater its resistance to oxidation
• Life cycle assessments evaluate the impact of products on the environment. They look at extracting/processing raw materials, manufacturing/packaging, use/operation and disposal.
• LCAs (Life Cycle Assessments) may be subjective and open to bias as some aspects cannot be measured as easily. For example, a number cannot be given for the long term effects of pollution on the environment. However, how much water, resource, energy are needed and waste produced can be measured.
• Recycling metals uses less energy than extracting them. Metals can be recycled by melting them down and reforming them into different products. Different metals usually have to be separated and sorted before recycling.

  The amount of separation needed before recycling depends on which metals are present.

  It also depends on what product you're making.

  For example, scrap steel and iron can be placed in a blast furnace together.

  This reduces the amount of iron that needs to be extracted from iron ore.
• chemical reactions are reversible, the use of the symbol ⇌ in equations and the direction of some reversible reactions can be altered by changing the reaction conditions
• Dynamic equilibrium is the state of a reversible reaction in which the rate of the forward reaction equals the rate of the backward reaction and the concentrations of reactants and products remain the same
• The formation of ammonia is a reversible reaction between nitrogen (extracted from the air) and hydrogen (obtained from natural gas) and it can reach a dynamic equilibrium.
• the conditions for the Haber process: temperature 450 °C, pressure 200 atmospheres, iron catalyst
• If the reaction is endothermic in one direction, it is exothermic in the other direction - in a reversible reaction.
• if the conditions change, the amount of reactants relative to products shifts. The system will then change to counteract this change and return to equilibrium. In other words, when a system is at equilibrium, any change in conditions will cause the system to try to prevent the change. Le Chatelier's Principle predicts how the system will respond to different changes.
• If the concentration of a reactant is increased, the forward reaction is favoured. If the concentration of a product is increased, the backwards reaction is favoured.
• If the temperature of the system is increased, the equilibrium shifts in the endothermic direction. If the temperature of the system is decreased, the equilibrium shifts in the exothermic direction.
• If the pressure is increased, the equilibrium shifts to the side of the equation with fewer molecules. If the pressure is decreased, the equilibrium shifts to the side of the equation with more molecules.