Some questions... (1 Viewer)

[Aerlinn]

Some random questions I was wondering whether someone could help me out with:
1. A hand-warmer purchased by campers and skiers consists of a sealed outer plastic bag and an inner perforated plastic bag containing powdered iron, water, salt and sawdust. When the inner bag is taken out and shaken it becomes hot because iron reacts with oxygen, producing iron (II) oxide and heat. Suggest why salt is included in the contents of the bag.
2. Sand and water are both used to smother fires. Which material would absorb the most heat from a fire? Why?
3. The moist brown coal used in coal-fired power stations in Victoria is not as good as the black coal used in power stations in New South Wales. Only about one-third of the substances present in brown coal are combustible. What other factor reduces the heat energy available from this fuel?
4. Water evaporating from the skin after swimming causes us to feel cool. Account for the fact that during this process the heat content of the water is increasing.
5. Comment on the prospects of replacing petrol with ethanol produced from sugar and using it as fuel for cars in the future.
6. Suggest one application in which coal is preferred to petrol and another in which petrol is preferred. Explain the reasons behind each choice of fuel.


:wave:

 

[wrxsti]

I dont think anybody will answer all of the questions there.... i can Answer Question 5) Ethanol can be produced from Renewable resources. It can be produced via Fermentation C6H12O6 --> C2h5OH + 2CO2. However this is a very energy intensive process as a lot of energy is needed in obtaining Ethanol to be used (Harvesting, Fractional Distillation). Ethanol almost always undergoes complete combustion due to the Oxygen atom present. its products Co2 and H20 are less polluting than petrol and can be utilised by plants. However there are some disadvantages. the current low price of Petrol means consumers will prefer petrol. Large ammounts of crops would be needed to sustain its operation. Also engines will corrode of Ethanol is used more than 15% . Specially modified engines need to be built to sustain it

Um. i sorta trailed off a bit. but i hope some of it helps :S

 

[xiao1985]

@aerlinn: you ought to get your teacher to slow down.... most of the questions you ask are .... way strange not entirely necessary to know for hsc =/

1) No idea... my guess is that salty water retains heat better than normal water. Therefore the heat loss will be minimised whilst hand warming is maximised.

2) Depends on their specific heat capacity. Though even if sand (silicon dioxide) has higher specific heat capacity, I would still say water siphons more heat out of flame. Because not only does it siphon heat when heats up, it siphons more heat when evaporated.

3) porosity? If oxygen can be pre-diffused into the coal, then the combustion maybe alot more complete.

4) This is easy: water gains heat, hence evaporate away. Where did it gain heat from? From you of course. therefore you feel cooler; water droplet (if it does feel) feel hotter.

5) as wrxsti said

6) adv of coal: no water produced, -> less greenhouse emission
petrol -> liquid, easy to transport

 

[Aerlinn]

3) 'oxygen pre-diffused into the coal'?
4) heheh
5) Thanx, wrxsti you seem to know quite a bit about that
6) One confusing thing: How does water contribute to the greenhouse effect?

Thanks to both of you ^^
PS.

ought to get your teacher to slow down

Yes she does get a bit carried away (she's one of those passionate chem people ^^) but it is interesting/ sometimes good background
~~~
Edit: (another round ^^)
1.Rather than spending money to further reduce gas emissions from their power stations, the Dutch government has decided to spend $35 million on the reduction of sulfur emissions in neighbouring Poland and $300 million in tropical countries to plant new trees in areas where trees have been felled. Why might the government have made this decision?
2. Brown coal power stations can generate a total of over 30 000 GWh of electrical energy each year. NSW's estimated 40 000 Mt of brown coal would last 3.2 * 10^3 years. In view of predicted patterns of energy use, would you expect this length of time to be higher or lower than the actual length of time before brown coal supplies are exhausted? Give reasons for your answer.
4. Why is electricity such a popular form of energy?
Something to do with cost? Or is it simply easily distributed?
5. Name 5 ways you could reduce you energy consumption away from the home.
6. a) What possible changes might lead to a greater use of nuclear power in Australia?
b) Why do you think that the use of solar water-heaters is not more widespread? Solar cars can be constructed and they are cheap to run. Why then do most people prefer petrol-driven cars?
7. Take ice-cream as an example of a commonly purchased item. List six ways in which energy has been used to provide the finished, wrapped product ready for you to eat.
:wave:

 

[xiao1985]

3) think this way. more oxygen = better burning. you learn that in production of materials. Therefore, porous coal lets more air (hence more oxygen) into it, and ensures a more complete combustion.

6) water absorbs IR. (and believe me. i know this first hand)

New questions:

1) hmmm sleeky lil bastards... want us poor science students justify their own course of action?!?!?

reduce SO2 emission = less acid rain. Less acid rain = less CO2 emitted into atmosphere (acid forces dissolved CO2 out of solution - namely in the ocean)

planting more trees = eat heaps more CO2 = less green house gas =O )

2 really depends .... how about you tell me what you thing?

3 missing... i shall assume you thought about it and know how to do it eh?!

4 cheap, easy, large scale production, versitile (maybe transformed into other form easily)

5 errrr i will name one: walk instead of driving?

6a killing all the greens. wait, that's gonna make it worse.
public lectures that safe nuclear usage is safe?!
b resistance to new technology (same as newton's law of intertia... resistance to motion)

7 hmmm yum! ice cream needs milk... to produce milk you need cows... you need to feed cows = grass... grass need fertilizers?
wrappers are papers need to be made... paper factory eats energy like crazy oO

you think the rest =)

 

[Aerlinn]

6) (I shan't ask how... )
1) just this bit

Less acid rain = less CO2 emitted into atmosphere

... huh?
2) Well I don't know... maybe if people realise coal's not going to be eternally there, they'll figure out other energy sources to use, but if they can't, or they have to avoid it for reasons like convenience or cost or things, the rate might stay constant. Though I'm not sure about current rates- have they increased over the past till now/ decreased/ stayed the same?
6a) Heheh. Does nuclear power have any advantages over other energy sources? (unique stuff?) Eg. i know it can be used for electricity, though what'd be the good/bad things about that compared to like say using coal or something?

Thankies ^_^

 

[xiao1985]

1) when acid goes into the water, it lowers water's capacity to absorbCO2. So acid rain can actually contribute global warming, as the run off water will increase sea acidity, making it less capable of absorbing CO2.

2) there's definitely a stronger push for greener energy over the past few years. energy demand is forever increasing, that's no doubt. Though it is to my belief that greener energy will be used in the future.

6) good thing: lots and lots of energy
badthing: waste last for couple millions of years, energy production is not efficient. by not efficient, i mean ratio of energy harvested / energy released.