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Physics, Chemistry and Biology: Post your doubts here!

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Don't worry :) Just do your best .. and be satisfied with ur effort in the end.. this is more imp. than getting high grades, (not saying that 's not important :D)
Stress would help u in no way bro (y)
yeah u are right but i have already started working hard and can u give me a site for bio notes
 
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in chemistry what is the difference between bonding in elements and bonding in compounds ? i also want detailed properties of each
 
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Well there are different types of bonding, For metallic elements its metallic bonding, which is due to the attraction forces between the positive nuclei and the free delocalised electrons...now you may already know that in metals the outer electrons are not in the last energy level/outer shell but rather delocalized! thus there is an attraction force between the positive metal ions and the free delocalized electrons! In Non metallic elements its covalent bonding, these covalent bonding are not very strong as covalent bonds in compounds, But as for your question, there aren't really much of difference in the bonding of elements and compounds ^^, As far as what we have in syllabus we didn't learn any! There are 2 types of bonding, Ionic [ Positive metals Cations and Negative Non-metal Anions ] and Covalent Bonding [ occurs with non-metals only ] Example in methane there are 4 covalent bonds!

Hope it helped and answered your doubt, if you have doubts still ask right away :D!
 
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Could someone please explain the process of drying gas to me? I read that when collecting a gas using downward delivery, the gas is dried through concentrated sulphuric acid.

How and why?
 
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Could someone please explain the process of drying gas to me? I read that when collecting a gas using downward delivery, the gas is dried through concentrated sulphuric acid.

How and why?
After collecting the gas, it is passed through concentrated sulphuric acid which is the dehydrating agent and absorbs the moisture of the gas, leaving it dry.
 
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I am uploading the recent Jun 2012 IGCSE 0625 Phyiscs paper 32. Can you please solve question 9b in it and then explain it to me too..??? Cos i m getting really confused..!!! Thanks.. :)
 

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Hey guys i have a doubt in the bio paper attached Q3-(e)
Can someone pls explain the answer to me?
 

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Hey guys i have a doubt in the bio paper attached Q3-(e)
Can someone pls explain the answer to me?

Because each enzyme has only one optimum pH, where as from graph we can see that there are two enzymes since the activity of enzymes are different. One works at pH 8 and the other works best below pH 8, I hope the answer is right and you understand what I mean :D
 
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In Chemistry:
Why would condensation of steam to water would be exothermic?
and why the evaporation of volatile liquid would be endothermic?
I think its because it depends on if its a physical or chemical change...(Correct me if I'm wrong)
**Who ever knows the answer you can explain some more examples on exothermic and endothermic reaction both from physical and chemical changes.
 
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In Chemistry:
Why would condensation of steam to water would be exothermic?
and why the evaporation of volatile liquid would be endothermic?
I think its because it depends on if its a physical or chemical change...(Correct me if I'm wrong)
**Who ever knows the answer you can explain some more examples on exothermic and endothermic reaction both from physical and chemical changes.
Condensation is exothermic because water vapours lose energy and turn into water molecules and evaporation is endothermic because water molecules gain energy and overcome the intermolecular forces of attraction and turn into steam.

Examples of endothermic reactions:
1. Decomposition reactions e.g calcium carbonate on heating decomposes to calcium oxide and carbon dioxide.
2. Electrolysis
3. Photochemical reactions (take light energy)
4. Dissolving of aluminium salts

Examples of exothermic reactions:
1. Displacement reaction (metal+acid --->salt +hydrogen)
2. Neutralisation reactions
3. Combustion reactions
All these reactions produce heat that's why they are exothermic.
 
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