Green chemistry Chem unit 2 Pt 8
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. What would you like to do?
List 5 things that could be done to make industries work in a more sustainable way?
- Use renewable raw materials
- Use renewable energy sources/ use less energy
- Ensure all chemicals involved are non-toxic as possible
- Ensure that products and waste are biodegradable or recyclable
- Catalysts - high atom economy and less waste.
Give one example of how energy efficiency can be improved in industry.
Pharmaceutical industry - use microwave radiation to heat reacting mixture directly. (Conventional heating systems are less efficient, heating systems in reaction vessels which then "pass on" heat to mixture.
Give 2 alternative energy sources to fossil fuels.
- Plant-based fuels (eg. bioethanol)
- Solar power, wind power, wave power etc.
If there is a process that involves harmful substances, you can either:
- Use alternative substances that are as non-toxic, not harmful to environment as possible etc.
- Redesign a process - means you can avoid using unsafe chemicals completely. (eg. instead of using harmful organic solvents, reactions can be carried out with one of the reactants acting as a solvent)
Why is it important in industry to have chemical reactions with high atom economy?
- Reduces waste
- Makes best use of resources (more efficient)
Why is it important to discover new catalysts?
- May speed up a reaction that was previously too slow to be used. (A new reaction could mean a new alternative)
- Might mean it is possible to have the same/better yield/rate using lower temperature and pressure. (So more energy efficient).
- Example of how industrial production of ethanoic acid (CH3COOH) became more efficient over the years.
Outline briefly how industrial production of ethanoic acid (CH3COOH) became more efficient over the years.
- 1. First made by oxidation of butane or naphtha. Needed 150-200oC, 40-50atm and cobalt catalyst. [Atom economy was low - 35% - because many other products were made too]
- 2. Process developed where methanol and carbon monoxide can be reacted. [100% atom economy. However, needed higher temp (300) and higher pressure (700atm) - cobalt iodide catalyst used - gave yield of about 90%]
- 3. Rhodium catalyst used with same reaction - less extreme conditions were needed. (improved yield of about 98%). Now, iridium iodide catalyst used - produces fewer by-products & more efficient use of resources.
What is the greenhouse effect?
- Electromagnetic radiation (mainly light, UV, IR) emitted by the Sun.
- Some IR is reflected off snow/ice etc, but some is absorbed by the Earth. The Earth then radiates energy as IR back towards space. Greenhouse gases in troposphere absorb some of this IR and re-emit it in all directions - including back towards Earth.
List 3 greenhouse gases.
- Water vapour
- carbon dioxide
Contribution of any particular gas to the greenhouse effect depends on:
- how much radiation one molecule of the gas absorbs
- the abundance/concentration of the gas in the atmosphere (concentration in ppm for example)
Why is there much movement to cut CO2 emissions when water vapour is a more greenhouse gas?
Becuase H2O conc in atmosphere has stayed relatively constant for many years, whereas conc of CO2 has increased dramatically.
Why have humans contributed to global warming?
- Over past 150 years, human population has risen dramatically, and become more industrialised - more demand for energy.
- Burning fossil fuels, growing farms of domestic animals (which release methane) all emit greenhouse gases.
- Deforestation reduces the number of trees which are used to absorb CO2 by photosynthesis.
List some ways climate has changed naturally in the past.
- Regular changes in Earth's orbit around Sun are linked to ice age cycles and interglacials in between.
- Various changes in Sun's activity (eg. sunspot cycles)
- Volcanic eruptions or meteor impacts have emitted large amount of smoke into atmosphere, causing significant global cooling.
What is anthropogenic climate change?
Climate change caused by human activity.
What is a carbon footprint?
Is the measure of the impact that human activities have on the environment in terms of the amount of greenhouse gases produced, measured in units of mass carbon dioxide.
What is carbon neutrality?
- A fuel is carbon neutral if it does not give an overall carbon emission into the atmosphere.
- If the amount of carbon dioxide absorbed when the raw material was grown, or when the fuel was formed, equals the amount of carbon dioxide produced when it's manufactured or burned. (eg. tree)
Petrol, bioethanol & hydrogen gas. Which are carbon neutral? Briefly explain.
- Petrol: not carbon neutral. CO2 released into atmosphere that was trapped in earth millions of years ago.
- Bioethanol: carbon neutral (more or less). Produced by fermentation of sugar. (but still carbon footprint if you look at whole process - fertilisers, powering agricultural machinery etc). (Also, in developing countries, food supply might be compromised for fuel)
- Hydrogen gas: carbon neutral (more of less). Water is the only waste product. (trouble with storing H2 gas safely tho)
What would you like to do?
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