Chemistry principles --- please help :)

Jan 2013
31
0
Hello everyone. I need help explaining these things. I have included the answers that I think I might know, but please help me with those and the blank ones. Thank you! :eek::eek:

Use chemical principles to explain each of the following:
(a) A pressure cooker is used to cook food at higher temperatures than can be achieved using a regular pot.


(b) Iron nails that are to be used outdoors are coated with zinc.
Iron is more prone to rusting, so the nails are coated with zinc to slow the process.

(c) Food kept in a refrigerator takes longer to spoil than food left out on a kitchen table.


(d) When water is left standing in plumbing during extremely cold weather, there is a danger that the pipes will burst.


(e) At low temperature and high pressure, a gas will deviate from ideal behavior.
 

Unknown008

CHF Hall of Fame
May 2010
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Mauritius
(a) Think about the relationship of water boiling and how pressure affects it.

(b) I'm not sure how much depth you are expected to give, but I would give at most 1 mark for this statement =P I was expecting an explanation of sacrificial protection.

(c) Talk about enzymes and reaction rates.

(d) What happens if the water freezes?

(e) What are the assumptions of an ideal gas' behaviour?
 
Jan 2013
31
0
(a) Think about the relationship of water boiling and how pressure affects it.

(b) I'm not sure how much depth you are expected to give, but I would give at most 1 mark for this statement =P I was expecting an explanation of sacrificial protection.

(c) Talk about enzymes and reaction rates.

(d) What happens if the water freezes?

(e) What are the assumptions of an ideal gas' behaviour?
a. I am not sure how water pressure affects water boiling...

b. What do you mean by sacrificial protection?

c. How do enzymes relate to this? And about the reaction rates--- does it spoil faster because many reactions will occur faster at higher temperatures?

d. Thank you! I know the answer now (I think): water expands when it freezes, so the pipes might burst if they aren't large enough to accommodate the ice :)

Thank you so much! :D
 

Unknown008

CHF Hall of Fame
May 2010
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Mauritius
(a) Hmm, I'm not speaking about water pressure, but about pressure (i.e. air pressure). Try to visualise the situation at molecular level: air molecules and water molecules. Now remember that at low pressure there are less air molecules about.

Now, at the surface of the water at high pressure, there are many air molecules hitting the surface. At lowe pressure however, there are less air molecules hitting the surface of water. Does this help seeing how pressure affects the boiling point of water?

(b) Ah, you could google that easily :) Basically, zinc is more reactive than iron and when both are placed in the same environment, zinc will corrode instead of iron because zinc is 'sacrificing' itself to 'protect' iron. Once all the zinc are gone, iron will start corroding.

(c) Yes, the rate of reaction is directly proportional to temperature, and enzymes speed up the rate of reaction at higher temperatures (as long as they don't get denatured).

(d) Exactly! :)

(e) This part?
 

Unknown008

CHF Hall of Fame
May 2010
1,658
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Mauritius
For the question c,in the low temperature, the microorganism is not easy to exist.
Instead, they love high temperature.
That's not true. 'High temperature' is ambiguous and I should perhaps remind you that cooking food kills micro-organisms.