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Reply 1
Wouldn't it be

2K(NO3)2 --> 2KNO + 2NO2 + O2?
Nitrate has a -1 charge, whereas potassium has a +1 charge.
Reply 2
tomster
Wouldn't it be

KNO3 --> KNO + O2?

Nitrate has a -1 charge, whereas potassium has a +1 charge.

ah of course! Didnt think of looking at it in terms of ions! thanks!
Reply 3
ArjunT
ah of course! Didnt think of looking at it in terms of ions! thanks!

Check it again.
Reply 4
cptbigt
Why have you put a 2 after the NO3? Its just KNO3, and the thermal decomposition of a nitrate makes a metal oxide, oxygen and nitrogen...

Sorry, I got confused.
Reply 5
ah wait no just checked my ion list and it says nitrate is kno3 so why doesnt it equal kno3 when it decomposes? the question says, when potassium nitrate is heated, it decomoposes to give potassium nitrate and oxygen. also why does it turn to K(NO3)2 i thought potassium was only +1 so it would stay the same?
Reply 6
ArjunT
ah wait no just checked my ion list and it says nitrate is kno3 so why doesnt it equal kno3 when it decomposes? the question says, when potassium nitrate is heated, it decomoposes to give potassium nitrate and oxygen. also why does it turn to K(NO3)2 i thought potassium was only +1 so it would stay the same?


You sure the question doesn't say it decomposes into potassium nitrite instead of nitrate?
Reply 7
cptbigt
Well the thermal decomposition of potassium nitrate is the equation I posted above. You sure the question doesn't say it decomposes into potassium nitrite instead of nitrate?

ah yes it does say nitrite, i guess i didnt read it properly... that makes a lot more sense. thanks
Reply 8
ArjunT
ah yes it does say nitrite, i guess i didnt read it properly... that makes a lot more sense. thanks


KNO3 -> KNO2 + 0.5O2 then :smile:
Reply 9
cptbigt
KNO3 -> KNO2 + 0.5O2 then :smile:

isnt it 4KNO3-->4KNO2+2O2 fully balanced?
Reply 10
ArjunT
isnt it 4KNO3-->4KNO2+2O2 fully balanced?


Why times everything by four? You can double it if you want to make whole numbers so...

2KNO3 -> 2KNO2 + O2

No reason to times it by 4.
mates, what r u TALKING abuot? alla group 1 nitrates are thermally stable they do NOT decompose... lol
Reply 12
anonymousboss
mates, what r u TALKING abuot? alla group 1 nitrates are thermally stable they do NOT decompose... lol


Lithium nitrate fully decomposes in the exact same manor as group 2 nitrates. The rest only partially decompose - into nitrites, unless high temperatures, which is what this question is about :smile:
anonymousboss
mates, what r u TALKING abuot? alla group 1 nitrates are thermally stable they do NOT decompose... lol


Wrong. I used to work with potassium nitrate a lot, and the fact it does thermally decompose was vital to what I used it for (fireworks). Lithium and sodium nitrates will too, and I suspect the others will eventually too.
It is difficult to decompose KNO3, but with enough heating it does form potassium nitrite and oxygen :smile:
Potassium nitrate is the major component of gunpowder - of course it decomposes to release oxygen THAT is why it was used in the first place...

Gunpowder 85% KNO3, 10% carbon, 5% sulphur (one recipe among the 1000's)
charco
Potassium nitrate is the major component of gunpowder - of course it decomposes to release oxygen THAT is why it was used in the first place...

Gunpowder 85% KNO3, 10% carbon, 5% sulphur (one recipe among the 1000's)


That mix has a big overload of KNO3 that would not be used. And carbon is never used.

Normal blackpowder would be 75 kno3, 15 charcoal, and 10 sulphur. Balance that decomposition if you have too much free time.
fisherman
And carbon is never used.


charcoal IS carbon :rolleyes:
charco
charcoal IS carbon :rolleyes:


The distinction is very important. Pure carbon, for example activated charcoal, graphite, or diamonds, would not make blackpowder good enough for anything. Charcoal contains volatile compounds, which massively speed up the burn rate. Willow charcoal is the traditional wood used, you get a big variation depending on the wood used.
fisherman
The distinction is very important. Pure carbon, for example activated charcoal, graphite, or diamonds, would not make blackpowder good enough for anything. Charcoal contains volatile compounds, which massively speed up the burn rate. Willow charcoal is the traditional wood used, you get a big variation depending on the wood used.


The distinction is important if you intend to make gunpowder. The OP's subject was potassium nitrate (not saltpetre). The answer was considered from a chemistry standpoint rather than alchemy or pyrotechnics.

Ye olde recipe for blackpowder

saltpetre - 85%
wood charcoal -15%
brimstone -10%

:yep: