chem - extracting metals + equilibria (4)

• Forwards yield the amount of product.
• The most reactive metals will react with cold water, producing a metal hydroxide and hydrogen.
• Fairly reactive metals react with acid MASH.
• Almost all metals react with oxygen, forming a metal oxide.
• The only metal that doesn’t react with cold water, acid, or oxygen is gold, which is extremely unreactive.
• You can determine the relative reactivity of some metals by observing if bubbles form when a reaction takes place.
• Displacement reactions can be used to determine if one metal is more reactive than another.
• More reactive metals form a cation (+) as they displace the less reactive one, causing the latter to lose electrons and be oxidised.
• Less reactive metals form atoms from anions (-) as they are displaced, gaining electrons and being reduced.
• Metals are arranged in order of their reactivity and non-metals hydrogen and carbon are often included in the reactivity series.
• The last element in the reactivity series is gold, which is found in the Earth as the metal itself but most metals are found as compounds that require chemical reactions to extract the metal.
• Oxidation and reduction are also known as gaining and losing O2.
• Metals that are less reactive than carbon can be extracted from their oxides by reduction with carbon, while metals that are more reactive than carbon can be extracted by electrolysis of molten compounds.
• Phytoextraction involves some plants absorbing metal compounds through their roots, concentrating these compounds into their leaves and burning these leaves to produce an ash that contains the metal compounds.
• Bacterial extraction involves some bacteria absorbing metal compounds and producing solutions called leachates which contain them, and scrap iron can be used to obtain the metal from the leachate.
• The less reactive a metal is, the more resistant it is to oxidation.
• Recycling is important for sustainable development as it requires less energy to melt and remould metals than it does to extract new metals from their ores.
• Mining ores is bad for the environment as it creates large quarries which produce noise pollution and dust.
• Recycling allows for waste metals to be reused, saving money, helping the environment and the supply of valuable raw materials.
• The Haber process is used to manufacture ammonia, which is used to produce nitrogen-based fertilisers.
• The reaction in the Haber process is reversible so ammonia breaks down again into nitrogen and hydrogen.
• The formation of ammonia is described as a reversible reaction between nitrogen (extracted from the air) and hydrogen (obtained from natural gas).
• In gaseous reactions, an increase in pressure will favour the reaction that produces the least number of molecules as shown by the symbol equation for that reaction.
• In some chemical reactions, the products of the reaction react to produce the original reactants, these are called reversible reactions.
• Lifetime assessment is carried out to assess the environmental impact of products in each of these stages: extracting and processing raw materials, manufacturing, packaging, use and operation during its lifetime, disposal at the end of its useful life, including transport and distribution at each stage.
• Nitrogen is obtained from the air and hydrogen may be obtained from natural gas.
• The direction of the reaction can be changed by changing the conditions, for example, if the forwards reaction takes place in hot conditions, lowering the temperature can cause the reverse reaction.
• The purified gases are passed over a catalyst of iron at a high temperature and a high pressure in the Haber process.
• The Haber Process: nitrogen + hydrogen ⇌ ammonia
• Equilibrium is reached when the rate of forward and backward reaction are equal, the concentration of reacting substances stays the same.
• The conditions for the Haber process include temperature 450°C, pressure = 200 atmospheres, and the use of an iron catalyst.
• If the concentration of one of the reactants or products is changed, the system is no longer at equilibrium and the concentration of all the substances will change until equilibrium is reached again.
• If temperature is increased: equilibrium moves in the direction of the endothermic reaction, if forwards reaction is endothermic and temperature is increased, equilibrium shifts right to produce more product.
• The raw materials for the Haber process are nitrogen and hydrogen.
• Some of the hydrogen and nitrogen reacts to form ammonia in the Haber process.
• Dynamic equilibrium is when once the forward + backward reaction reach equilibrium, they keep going.
• The ⇌ symbol is used to show that a reaction is reversible.
• The relative amounts of all the reacting substances at equilibrium depend on the conditions of the reaction, if a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract the change.
• If temperature is decreased: equilibrium moves in the direction of the exothermic reaction.
• Allocating numerical values to pollutant effects is less straightforward and requires value judgements so LTA is not a purely objective process.