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Chemistry: Post your doubts here!

knowitall10

knowitall10

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Jinkglex said:
Im in A2 :eek: why do you ask? and alright thanks :D I was just confused because i keep involving Lattice energy in here, which is strictly A2 :p
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Oh i was asking cuz depending on that, i'd ask you my questions... firstly... i do not understand how on earth to calculate the enthalpy change using bon enthalpies- more precisely i'm always confused which side is bond breaking and which is bond forming... i know this is AS stuff but i hate the AS part that comes in p4... the manhoos examiners can't make it any harder :/
 
knowitall10

knowitall10

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PANDA- said:
You got it wrong there, all alkali are bases bot not all bases are alkaline. This is because alkali's are bases which are dissolved in water, like NaOH(aq) for example.
Reactivity mainly depends on the effective nuclear charge, atomic radius, and molar mass (not really sure about molar mass lol).
Click to expand...
thanks Panda... i'm ashamed to mention i'm in A2 now :p
 
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Manobilly

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daredevil said:
Kc is calculated using the formula
([C]^c x [D]^d )/([A]^a x ^b)

for a reaction: -
aA + bB --> cC + dD

where the small letters represent the number of moles of the substances (capital letters are substances)
x is the sign of multiplication
and do not use round brackets at all!! i used them just to show that all the products were in the numerator and theproducts are all in denominator
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Can you show the full working of the question.
 
Dania_Yz

Dania_Yz

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I cant understand the mass spectrometer, my teacher didn't teach us anything about it.. Help!
 
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Jinkglex

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Bon enthalpies? You're going to have to elaborate on that :p

As far as bond breaking and making is concerned, look at the following reaction:

CO + 1/2O2 -> CO2.

Simple enough right? Now all you have to remember is before reacting all atoms must go into their atomic gaseous state. Thus here, the O2 molecule will be broken into 2 O ATOMS. This is bond BREAKING. Then, the O atom will react with the CO molecule to make a CO2 molecule. During this, the C bonds with the extra O atom. And this is bond MAKING. Bond breaking is always ENDOTHERMIC because it always requires energy. Thus, Bond making is automatically exothermic.

Think of bond making as a bank transaction. When you're MAKING a bond you're putting in money. Now theres less money [Energy] in your pocket [surroundings], but more money [Energy] in your bank account [between bonded atoms]. Likewise when you make a withdrawal or BREAK a bond, there is less money in your bank account, but more in your pocket.
 
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Jinkglex

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Mass spectrometer for AS is simple enough. You ionize/vaporize a sample, throw electrons at it until it loses an electron going into the +1 state, and pass it through electric field [to streamline it] and magnetic field [to make it acquire a circular pathway]. Then you change the magnetic field to make it hit your detector, giving you a mass/charge ratio against percentage abundance of said peak. :p
 
knowitall10

knowitall10

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Jinkglex said:
Bon enthalpies? You're going to have to elaborate on that :p

As far as bond breaking and making is concerned, look at the following reaction:

CO + 1/2O2 -> CO2.

Simple enough right? Now all you have to remember is before reacting all atoms must go into their atomic gaseous state. Thus here, the O2 molecule will be broken into 2 O ATOMS. This is bond BREAKING. Then, the O atom will react with the CO molecule to make a CO2 molecule. During this, the C bonds with the extra O atom. And this is bond MAKING. Bond breaking is always ENDOTHERMIC because it always requires energy. Thus, Bond making is automatically exothermic.

Think of bond making as a bank transaction. When you're MAKING a bond you're putting in money. Now theres less money [Energy] in your pocket [surroundings], but more money [Energy] in your bank account [between bonded atoms]. Likewise when you make a withdrawal or BREAK a bond, there is less money in your bank account, but more in your pocket.
Click to expand...
Nice... thanks.. it explained everything (y)
 
knowitall10

knowitall10

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Jinkglex said:
Mass spectrometer for AS is simple enough. You ionize/vaporize a sample, throw electrons at it until it loses an electron going into the +1 state, and pass it through electric field [to streamline it] and magnetic field [to make it acquire a circular pathway]. Then you change the magnetic field to make it hit your detector, giving you a mass/charge ratio against percentage abundance of said peak. :p
Click to expand...
Mass spectrometry is only in A2.. what are you guys talking about?
 
Jiyad Ahsan

Jiyad Ahsan

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PANDA- said:
You got it wrong there, all alkali are bases bot not all bases are alkaline. This is because alkali's are bases which are dissolved in water, like NaOH(aq) for example.
Reactivity mainly depends on the effective nuclear charge, atomic radius, and molar mass (not really sure about molar mass lol).
Click to expand...

yep thats right^

btw panda... i need a bit of help
in organic chemistry we have oxidising agents KMnO4 and K2Cr2O7
and some reactions state using only one.. is there a difference? similarly LiAlH4 and NaBH4..
 
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