Chemistry - Speed of Reaction
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Liquid paraffin burns slowly in air but paraffin spray burns rapidly. Explain. (particle size?)
Flour dust can cause explosions in a flour mill. Explain (particle size)
When a piece of a raw liver is dropped into H2O2, there is a rapid reaction and oxygen gas is liberated. (Do you explain in terms of catalyst?)
Not sure about the factors affecting the 3 reactions above. Please tell me whether my basis for explanation is correct.(no necessary need to explain though, just want to know if I have chosen the factor correctly)
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Liquid paraffin burns slowly in air but paraffin spray burns rapidly
i think this is because of the surface area.
the rest correct already :) should be yeah
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Originally posted by jesslyn1992:
i think this is because of the surface area.
the rest correct already :) should be yeah
Ah yes, surface area is referring to particle size. When particle size decreases, surface area increases thus an increase in reaction speed due to more effective collisions. Thank you! -
You're both right. Smaller particle size = larger surface area (to volume ratio) = increased surface area of reactants exposed and available for the reaction = increased frequency of effective collisions = increased rate of reaction.
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Originally posted by UltimaOnline:
You're both right. Smaller particle size = larger surface area (to volume ratio) = increased surface area of reactants exposed and available for the reaction = increased frequency of effective collisions = increased rate of reaction.
Does H2O2 or raw liver act as catalyst? It looks like the raw liver from description. -
And yes, the liver contains the enzyme catalase, which increases the rate of reaction by lowering the activation energy required for the redox disproportionation decomposition reaction of hydrogen peroxide to water and oxygen.
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Wikipedia on Catalase (present in high concentration in human and animal livers, since one of the main function of the liver is detoxification) :
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I have another question for you guys here.
It is said that during industrial prepartion of alcoholic drinks, sugar or starch is converted into alcohol with the help of enzyme. At this stage, the temperature is not allowed to go aboove 21 deg cel or below 14 deg cel.
I understand the enzyme's role as catalyst. However why is it that temperature is contained within a certain range? Is it because the catalyst is functional at certain temperature ranges? (not sure if my explanation is correct)
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Originally posted by bonkysleuth:
I have another question for you guys here.
It is said that during industrial prepartion of alcoholic drinks, sugar or starch is converted into alcohol with the help of enzyme. At this stage, the temperature is not allowed to go aboove 21 deg cel or below 14 deg cel.
I understand the enzyme's role as catalyst. However why is it that temperature is contained within a certain range? Is it because the catalyst is functional at certain temperature ranges? (not sure if my explanation is correct)
This is the reason why it is advantageous to have a teacher or tuition teacher (eg. me!) with background in both Chemistry and Biology.
Strictly in terms of Chemistry, you would want temperature to be as high as possible, as long as not exceeding the optimum temperature for the enzyme (else the heat energy would overcome the forces, particularly hydrogen bonds, that give the enzyme a precise structural configuration required for the enzyme to function; the enzyme would denature). This optimum temperature range is different for every enzyme, but for the many (not all!) enzymes studied under the 'O' and 'A' level syllabus, it is usually close to 40 deg C.
Now, for this context of alcoholic (ethanolic) production by enzymatic fermentation of carbohydrates, such as using the yeast fungus, I will not give exact numerical values for optimum temperature and such, because different sources, different industrial companies, may use slightly different temperature ranges.
But what I will highlight here, to contribute to your understanding of this matter, is an important point that many students, teachers, and textbooks neglect, and usually themselves do not realize or understand.
It is this :
The reason why a seemingly low temperature (eg. 20+ deg C), significantly lower than the optimum temperature for the yeast enzymes involved (eg. 30+ deg C), is said to be the 'optimum temperature' for ethanol production via carbohydrate fermentation, is because of biology - the enzymes may function faster at a higher temperature, but the yeast fungus itself, does not.
The optimum temperature for yeast to reproduce (you can't say "have sex", since they reproduce asexually), is actually significantly lower than the optimum temperature for the enzymes within yeast that are involved in the fermentation of alcohol to produce ethanol.
So it's a trade off. At lower temperatures, enzymes work slower, but yeast reproduces faster, and hey, experimental evidence indicates that (think about the exponential reproductive capability of yeast fungus, akin to bacteria!) the trade off is well worth it - you get a lot more ethanol produced if you lower the temperature and make your yeast employees happy and busy reproducing! More yeast = more ethanol produced!
Another example of how valuable it is to have background in multiple disciplines (for myself, Chemistry and Biology), is how I recall both the Biology teachers and the Chemistry teachers needed my help to explain the following science mystery to students :
"Why is it that banana kept in the cold fridge ripens faster than banana kept on the warm kitchen table?"
Well, ok, this riddle is actually a red herring, and not so much about the advantages of being multidisciplinary. But it's still a fun riddle nonetheless. Ask your friends in school to solve this riddle!
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factors are correct.
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Hmm. interesting thread. A question for all to ponder.
When excess magnesium ribbon is added to dilute HCl acid, the reaction soon becomes slower and finally stops. Which of the following statement best explains this?
- concentration of HCl acid is decreasing until it becomes zero
-the magnesium ribbon is gradually c\becoming smaller.
-the magnesium ribbon is slowly being covered with an insoluble layer of MgCl2
- the temperature of the reaction mixture is gradually increasing until a maxiumum temperature is finally reached.
Very very relvant to topic on speed of reaction. I think it is the 3rd choice... but can MgCl2 be insoluble? Weird, this is contrary to the solubility table rules. Any suggestions?
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Originally posted by bonkysleuth:
I have another question for you guys here.
It is said that during industrial prepartion of alcoholic drinks, sugar or starch is converted into alcohol with the help of enzyme. At this stage, the temperature is not allowed to go aboove 21 deg cel or below 14 deg cel.
I understand the enzyme's role as catalyst. However why is it that temperature is contained within a certain range? Is it because the catalyst is functional at certain temperature ranges? (not sure if my explanation is correct)
chemical catalysts dont need to be kept at a certain temperature, but biological catalysts (enzymes, for example) need to be kept at a certain temperature.
this is because if the temperature of the biological catalysts is too high, the catalyst might be denatured, it'll lose it's 3D shape (refer to the key and lock thingy in biology)
i take chem and bio. that's what my teacher told me
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Originally posted by anpanman:
Hmm. interesting thread. A question for all to ponder.
When excess magnesium ribbon is added to dilute HCl acid, the reaction soon becomes slower and finally stops. Which of the following statement best explains this?
- concentration of HCl acid is decreasing until it becomes zero
-the magnesium ribbon is gradually c\becoming smaller.
-the magnesium ribbon is slowly being covered with an insoluble layer of MgCl2
- the temperature of the reaction mixture is gradually increasing until a maxiumum temperature is finally reached.
Very very relvant to topic on speed of reaction. I think it is the 3rd choice... but can MgCl2 be insoluble? Weird, this is contrary to the solubility table rules. Any suggestions?
Which is the limiting reactant and which is the excess reactant? There's your answer on why the reaction slows and finally stops. -
Originally posted by anpanman:
Hmm. interesting thread. A question for all to ponder.
When excess magnesium ribbon is added to dilute HCl acid, the reaction soon becomes slower and finally stops. Which of the following statement best explains this?
- concentration of HCl acid is decreasing until it becomes zero
-the magnesium ribbon is gradually c\becoming smaller.
-the magnesium ribbon is slowly being covered with an insoluble layer of MgCl2
- the temperature of the reaction mixture is gradually increasing until a maxiumum temperature is finally reached.
Very very relvant to topic on speed of reaction. I think it is the 3rd choice... but can MgCl2 be insoluble? Weird, this is contrary to the solubility table rules. Any suggestions?
hm.. excess magnesium ribbon.. that means if the reaction stops, it'll be because there's not enough magnesium to react with the other reactant, HCl, anymore.
so i guess the answer is A :) HCl is used up, thus magnesium cannot react with anything already..
MgCl is soluble, so the answer cannot be C (i think).. the layer that Mg usually formed is with something which contains O2-; they form MgO (which is insoluble)
i hope it's right. idk, coz im only sec4 this year. ha ha
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I am a little confused over the reaction between 2 substances, say HCl and sodium thiosulphate solution.
For example if you were to conduct this experiment in 2 conical flasks(1 big, 1 small) in which concentration of the acid and that of sodium thiosulphate solution is the same and the volume (10 cm3 of HCl added to 50cm3 of Na2S2O3) is the same, would the reaction be FASTER in the smaller flask?
Going back to the theory of rate of reaction. Since concentration is the same, there shouldn't be any increase/decrease in speed of reaction. However, one thing is to be noted. There are definitely more particles per unit volume in the smaller conical flask.(wouldn't this increase rate of reaction in smaller conical flask?)
And with regards to anpanman's question, I was thinking, even if HCl is the limiting reactant, would concentration actually fall during a reaction? Isn't it the volume that decrease and not the concentration?
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Originally posted by bonkysleuth:
I am a little confused over the reaction between 2 substances, say HCl and sodium thiosulphate solution.
For example if you were to conduct this experiment in 2 conical flasks(1 big, 1 small) in which concentration of the acid and that of sodium thiosulphate solution is the same and the volume (10 cm3 of HCl added to 50cm3 of Na2S2O3) is the same, would the reaction be FASTER in the smaller flask?
Going back to the theory of rate of reaction. Since concentration is the same, there shouldn't be any increase/decrease in speed of reaction. However, one thing is to be noted. There are definitely more particles per unit volume in the smaller conical flask.(wouldn't this increase rate of reaction in smaller conical flask?)
And with regards to anpanman's question, I was thinking, even if HCl is the limiting reactant, would concentration actually fall during a reaction? Isn't it the volume that decrease and not the concentration?
Very simple.What's concentration?
Simply speaking, the number of particles per unit volume right?
The concentration is not the same if the flasks are of different sizes and yet the number of particles inside remain the same right?
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Funny. Why you 'O' level guys think so much? Haha.
When I was young, as long as I get the answer and get the A, I really couldn't be bothered.