The Naked Scientists

The Naked Scientists Forum

Author Topic: Calcium Hydroxide  (Read 8317 times)

Offline sumesh25

  • First timers
  • *
  • Posts: 3
    • View Profile
Calcium Hydroxide
« on: 04/11/2007 04:09:28 »
is there any catalyst to decompose calcium hydroxide at lower temperature? In general calcium hydroxide decompose around 580 degree c. I am looking for some catalyst to decompose it less than that temperature. Any information would be highly appreciated.
Thanks in advance.
Sumesh


 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8668
  • Thanked: 42 times
    • View Profile
Calcium Hydroxide
« Reply #1 on: 04/11/2007 12:21:29 »
The simple answer is no. A catalyst only affects the rate of a reaction and that's not the issue here. About 580C is the temperature where the water vapour comming off has a pressure of 1 atnosphere.
You coud decompose it at a lower temperature in a vacuum.
 

Offline sumesh25

  • First timers
  • *
  • Posts: 3
    • View Profile
Calcium Hydroxide
« Reply #2 on: 05/11/2007 23:02:51 »
Catalysts do lower the temperature. If you remember the preparation of Oxygen gas, Manganese Dioxide is used to lower the temperature of the decomposition of Potassium Chlorate.

i dont know much chemistry but how chemist explain the above statement?
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8668
  • Thanked: 42 times
    • View Profile
Calcium Hydroxide
« Reply #3 on: 06/11/2007 19:42:18 »
Even at room temperature KClO3 decomposes; it's just that the rate is far too low to observe.
If you want to get a useful rate of reaction you need to heat it.
If you add a catalyst the reaction is faster (at any given temperature) so, with a catalyst you don't need to heat it as much in order to get a decent rate of reaction.
 

Offline sumesh25

  • First timers
  • *
  • Posts: 3
    • View Profile
Calcium Hydroxide
« Reply #4 on: 08/11/2007 16:45:46 »
it means calcium hydroxide only start decomposition when temperature reaches 580C. Below this temperature, for instance 250C, there is zero decomposition. I would not have problem with rate of reaction. I need lower temperature eventhough the rate of reaction is very slow.
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8668
  • Thanked: 42 times
    • View Profile
Calcium Hydroxide
« Reply #5 on: 08/11/2007 21:52:25 »
It's not quite that simple.

The rate of decomposition of the hydroxide might be reasonable enough even at 100C.
The question is how far does it go. After all the reaction runs the other way if you add water to the oxide.

If you heat some the stuff will start to decompose- in much the same way that if you heat water it will evaporate. If you were to do this in a closed vessel (empty of air) then the steam would build up. The reaction will stop when the pressure reaches some value. At higher temperatures you will get a higher pressure- but the reaction will still stop. This is because, with enough steam there, the reverse reaction is just as fast as the forward one.

The temperature of 580C is the temperature at which the pressure of the steam is 1 atmosphere.

At that temperature the escaping steam can push the air out of the way and the rate of the forward reaction increases. A bit like water reaching its boiling point.

The only way to get a decent rate of reaction at a lower temperature (and there's no real way to guarantee it would be as fast as you want) would be to put the stuff in a vacuum chamber.
 

Offline x_sunjay

  • First timers
  • *
  • Posts: 5
    • View Profile
Calcium Hydroxide
« Reply #6 on: 13/11/2007 11:31:16 »
What if he were to remove the build up of steam as he decomposes the hydroxide. Maybe he could use a fan a blow the steam away or he could do it in a well ventilated area?
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8668
  • Thanked: 42 times
    • View Profile
Calcium Hydroxide
« Reply #7 on: 13/11/2007 19:38:12 »
That would help.
 

The Naked Scientists Forum

Calcium Hydroxide
« Reply #7 on: 13/11/2007 19:38:12 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums