Physics, Chemistry and Biology: Post your doubts here!

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slisjunknown said:
Please help guyz I've got a doubt in the question no. 5 c(i)
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w13_qp_31.pdf
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The alkenes split at the double bond. So propene has 3 carbon atoms; splits to give two carboxylic acids methanoic acid (1 C) and ethanoic acid (2 C) when oxidized.
Propanoic and ethanoic acid together have 5 C atoms, so the alkene pentene would need to be oxidized to form these two.
And for the formation of only ethanoic acid, you'll need an alkene with 2 Cs on either side of a double bond, and that's but-2-ene.
 
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karimalaaa

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I had a problem with my surname in statement of entry then I changed it but the bio paper 1 was printed with the old one elsamdoni instead of el samadoni. I told the invigilators and the supervisor but they told me no problem as centre and candidate numbers and signature are written correctly but iam really unsure about what they told me .do u think there is a problem?
 
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karimalaaa said:
I had a problem with my surname in statement of entry then I changed it but the bio paper 1 was printed with the old one elsamdoni instead of el samadoni. I told the invigilators and the supervisor but they told me no problem as centre and candidate numbers and signature are written correctly but iam really unsure about what they told me .do u think there is a problem?
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No problem at all. Even i encountered a similar case, and i was so, SO tensed. But apparently, you know, the invigilators verify and reverify the candidate numbers, names and stuff before sending them across. Also, examiners check candidate numbers, not names, which even if have gone wrong (hardly any chance to), the entire bundle of papers from the center number is seen, and the missing number is tagged to the particular goofed up person, as a last resort maybe. Dw. You have your candidate number.
 
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Atharva Joshi said:
Subject : Chemistry

Can somebody explain the Lechatlier's principle and what happens during an exothermic and an endothermic reaction.
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The Le Chatelier's principle can be stated as:

When a system at equilibrium is subjected to change in
1. concentration,
2. temperature,
3. volume, or
4. pressure,
then the equilibrium readjusts itself to counteract the effect of the applied change and a new equilibrium is established.
The chemical system will attempt to partially oppose the change affected to the original state of equilibrium. In turn, the rate of reaction, extent and yield of products will be altered corresponding to the impact on the system.

In chemistry, the principle is used to manipulate the outcomes of reversible reactions, often to increase the yield of reactions.
Read this : http://www.chemguide.co.uk/physical/equilibria/lechatelier.html
 
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Atharva Joshi said:
Subject : Chemistry

Can somebody explain the Lechatlier's principle and what happens during an exothermic and an endothermic reaction.
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Exothermic reactions transfer energy to the surroundings. Endothermic reactions take in energy from the surroundings.

Reversible reactions are where the products can react to remake the original reactants. If the forward reaction is exothermic, the reverse reaction is endothermic.
 
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