Chem investigation task 6 Flashcards
What type of reaction is the Haber process for ammonia production? write the formula
N2(g)+3H2(g)–><–2NH3(g)
ΔH= -92kJmol-1
How is nitrogen obtained
(detailed version)
-Obtained in the atmosphere (making up 78% of the air)
-Separated from other components through liquefying the air
-followed by fractional distillation of the liquefied air (separates components of a mixture according to their different boiling points)
how is hydrogen obtained
-source depends on several factors including availability and cost of raw materials and energy.
-fossil fuels are the most common source, with natural gases (methane primarily) being simplest and cheapest.
-hydrogen is obtained via steam reforming/steam methane reforming
how is hydrogen obtain via steam methane reforming
include formula of reactions
-methane from natural gas is heated, with steam, usually with a catalyst, to produce a mixture of carbon monoxide and hydrogen
- the two-step reaction is endothermic, requiring heat for the reaction to occur.
Step 1: CH4(g)+H2O(g)–><–CO(g)+3H2(g)
Step 2: CO(g)+H2O(g)–><–CO2(g)+H2(g)
what is the by-product of hydrogen production? how is it negative?
include reaction formula
significant amounts of carbon dioxide (CO2) is produced as a by-product which is not used during the production of ammonia.
Step 1: CH4(g)+H2O(g)–><–CO(g)+3H2(g)
Step 2: CO(g)+H2O(g)–><–CO2(g)+H2(g)
As a result, the CO2 produced alongside hydrogen is manufactured as waste, entering the atmosphere increasing global warming and other environmental dilemmas.
What are the actual conditions of the Haber process
Temperature: industrial plants use moderate temperatures, between 350 °C and 550 °C
Pressure: high, varying between 100 and 250 atmospheres/atm
Catalyst presence: use of porous iron/iron oxide (Fe3O4) catalyst allows use of moderate temperatures while producing reasonable reaction rate required.
Describe the ideal conditions of the Haber process
Temperature would be higher to allow for larger reaction rate
Catalyst is present to allow for increased reaction rate in the presence of lower temperatures to decrease cost and increase efficiency
Partial pressure of gaseous reactants is higher (higher pressure)
to allow higher reaction rate to be achieved, ensuring a high yield the gives the plant greater productivity and reduces waste
Describe the reasoning for the changing conditions of temperature in the Haber process
-due to ammonia production=exothermic reaction, increasing the temperature will lead to a higher reaction rate, backwards (endothermic) more than forwards, but the value of equilibrium constant and eqm yield of ammonia will decrease as a result
-moderate temperatures are used ideally to ensure that the yield is sufficient while maintaining a reasonable reaction rate
Describe the reasoning for the changing conditions of pressure in the Haber process
-increasing pressure causes system to shift to side of equation with fewer gaseous particles to reduce pressure
-4 gaseous reactant particles and 2 gaseous product particles in equation, so system shifts to the right at an increase in pressure
-increases forward rate and the amount of ammonia present at equilibrium
-therefore, high pressure causes increased equilibrium yield and increased reaction rate
Describe the reasoning for the condition of a catalyst in the Haber process
-the presence of a catalyst allows for increased reaction rate due to supplying alternative pathway for reaction to take place that requires lower activation energy
-it will have no effect on the equilibrium yield but allows for the use of moderate temperatures while producing the reasonable reaction rate required
-saves money by using lower temperature while producing more products therefore profit
What are the stage of sulfuric acid production?
write the three reactions
Stage 1: Sourcing or producing sulfur dioxide
S(l) + O2(g)–>SO2(g) ΔH=-297kJmol-1
Stage 2: Converting sulfur dioxide into sulfur trioxide
2SO2(g) + O2(g)–><–2SO3(g) ΔH=-197kJmol-1
Stage 3: Absoprtion of sulfur trioxide and conversion to sulfuric acid
SO3(g) + H2O(l) H2SO4(aq) ΔH=-130kJmol-1
Describe stage one of the contact process to produce sulfuric acid? how is sulfur dioxide sourced?
Obtained from;
-Combustion of sulfur recovered from natural gas+crude oil (fossil fuel refining)
S(l) + O2(g)–>SO2(g)
-If extracted sulfur used as raw material, molten sulfur sprayed under pressure into furnace where it burns in air to =sulfur dioxide gas. High SA of sulfur spray allows rapid combustion
Gas is cooled for next stage. If sued as raw material then must dried (by bubbling though concentrated sulfuric acid) and pumped directly into next stage of process
-Smelting of sulfide ores of copper, zinc, or lead
Describe stage two of the contact process to produce sulfuric acid?
Main equilibrium step occurs in converter where sulfur dioxide is oxidised by oxygen to form sulfur trioxide gas
2SO2(g) + O2(g)–><–2SO3(g) ΔH=-197kJmol-1
Describe stage three of contact process to produce sulfuric acid?
Interpret the differing reaction pathway due to change in initial reaction
SO3(g) + H2O(l) –> H2SO4(aq) ΔH=-130kJmol-1
-direct reaction with water not used because ^heat is produced that a fine mist of acid is produced. (difficult to collect as a result)
Instead, passed into concentrated sulfuric acid in an absorption tower.
1. SO3(g) + H2SO4(aq) –> H2S2O7()
Sulfur trioxide gas dissolves almost completely in acid to form oleum (liquid)
2. H2S2O7(l) + H2O(l) –>2H2SO4(l)
Oleum then mixed with water to produce sulfuric acid
what is the by-product/product of sulfuric acid? how is it negative?
include reaction formula
Unreacted SO2 in stage 3 can be recycled back into converter in process call double absorption
Must occur because SO2 emissions into atmosphere can =formation of acid rain. The SO2 reacts with H2O in rain/clouds to form sulfurous acid (weak acid) and donates proton to water to form hydrogen sulfite ions
SO2(g) + H2O(l) –><– H2SO3(aq)
H2SO3(aq) + H2O(l) –><–HSO3-(aq) + H3O+(aq)
Sulfur dioxide gas can also corrode metals and is harmful to the growth of plants and aquatic animals
What are the actual conditions of the contact process
Lowered pressure, atmospheric, used in the contact process due to the cost of maintaining a high pressure outweighing the added benefits of higher reaction rate and higher yield
Moderate temperature of 400-500 °C used in conjunction with Vanadium oxide (V2O5) catalyst
What are the ideal conditions of the contact process
Higher pressure in order to increase the reaction rate and have a higher equilibrium yield
Higher temperature would allow for high reaction rate
Catalyst is present to allow for increased reaction rate in the presence of lower temperatures that may not have required activation energy levels
Describe the reasoning for the changing conditions of pressure in the contact process
-Increasing pressure would cause for great reaction rate and higher yield
-Due to the high cost of maintaining pressure outweighing the benefits of an increased reaction rate and higher yield, atmospheric pressure is used instead
-pressure is dangerous in larger amounts
Describe the reasoning for the changing conditions of temperature in the contact process in conjunction with a catalyst
show equations
-due to contact process being exothermic overall, increase in temperature effects backward, endothermic reaction more than the forward.
-a high reaction rate would be produced but the value of equilibrium constant and eqm yield will decrease as a result.
- Therefore, moderate temperature is used in conjunction with Vanadium oxide (V2O5) catalyst to ensure high enough reaction rate achieved while producing reasonable yields
- to ensure gases are kept at desired temperatures, the gas mixture is cooled as it passes from one catalyst to next.
Describe how ibuprofen production reflects the principles of green chemistry
-Initial production of ibuprofen utilised the ‘brown’ synthesis pathway, utilising 6 steps in which only 40% of atoms in reactants ending up in final product
-New ‘green’ synthesis pathway developing involving only 3 significant steps
-Maximise atom economy: 77% of atoms from reactants resulted in final product instead of 40%. Example of how the newly designed synthesis has final product containing the max proportion of starting materials causing few wasted atoms
-Prevent waste: 99% of atoms may also be used by regenerating and reusing some reactants to avoid unnecessary waste
Describe how extraction of gold reflects the principles of green chemistry
standard method for gold extraction/ refining involves gold cyanidation -gold leached from the ore as a water-soluble cyanide complex
-Chemists at Curtin University developed gold extraction process substituting cyanide for non-toxic glycine.
-Aqueous solutions of cyanide degrade in sunlight = harmless substances may persist in environment making overall refining process costly.
-Unlike cyanide, glycine is environmentally benign, cheaper, and recyclable. It;
-Reduces environmental danger that mine tailing present, it is just as accessible as cyanide, and reduces need for vast open cut mines such as super pit
-Design less hazardous chemical synthesis, safer chemicals and products and use safer solvents and reaction conditions
What does alcoa aluminum refinery produce primarily as waste?
What is it’s negative impact
-Alcoa Aluminium refinery in Kwinana (AAK) produces red mud as main waste. Tailings produced after alumina extraction consisting of highly alkaline slurry of sediment particles and wastewater.
-Poses risk to surface and ground water resources
How does the relationship between AAK and nearby CBS plant reflect principles of green chemistry
-Collaborative exercise between AAK +CBS ammonia plant helps prevent pollution by AAK utilising CBS toxic by-product to minimise/eliminate waste
-Hydrogen required in Haber process produced by steam reforming methane (by-product of CO2) which neutralises high alkalinity of AAK’s tailings in process =carbonation.
-Reduces pH to level of surrounding soils
-Tailing residue form carbonation is beneficial soil additive known as Alkaloam
-disposed of safely
-Provides a number of benefits to a typical Perth soil (raising pH and increasing phosphate retention by 70%)
Describe how removing a product in Haber process would effect yield and reaction rate
- removing product will increase forward rate as equilibrium will shift to increase the amount of products
-this will cause a net forward reaction
Describe how the haber process occurs
What is the ultimate yield
-nitrogen and hydrogen are compressed and pumped into reactor
-reactor contains several layers of iron oxide catalyst
-mixture then passed through another vessel where it is cooled, and gaseous ammonia is liquified and collected
-unreacted nitrogen and hydrogen compressed again and pumper through reactor
-continual removal of ammonia product causes increase in the forward rate of reaction
-gives ultimate yield of 98%
Describe how the contact process occurs
What is the ultimate yield
