When calculating eq. constant...

rparjf022 · 1 Oct 2008, 1:41 PM

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When you calculate the equilibrium constant (K), do you need to put in units? Some people around me are saying yes and others no... so I'm pretty confused.

danz90 · 1 Oct 2008, 2:05 PM

The equilibrium constant is only measuring the extent to which the forward reaction is occuring/favoured at particular conditions.
If conditions such as pressure and temperature of the reaction are given, make sure you answer in this format:

Kc = __ at T°C and ___kPa or ___atm

For calculating, just sub in the equilibrium concentrations of the products and reactants into the equilibrium expression. Always round off to the lowest significant figure present in the question.

henry08 · 1 Oct 2008, 4:05 PM

The syllabus dotpoint specifically states that no units are needed for equilibrium constant.

gezzill · 8 Oct 2008, 1:22 PM

mol/L i think, unless it specifically says.

minijumbuk · 8 Oct 2008, 1:26 PM

No units.

tommykins · 8 Oct 2008, 1:27 PM

Quote:

Originally Posted by minijumbuk

No units.

This.

danz90 · 8 Oct 2008, 7:55 PM

There's no units for equilibrium constant... its just a figure that shows the extent to which the forward reaction in an equilibrium reaction is favoured, at a particular temperature.

cwag · 9 Oct 2008, 8:43 PM

still on the same topic....iv seen many calculations in books where they don't seem to involve any solids or liquids in the K expression.....are they wrong. i thought it was plainly [products]/[reactants] no exceptions.?

minijumbuk · 9 Oct 2008, 8:49 PM

Umm, I think it's only aqueous and gas.

cwag · 9 Oct 2008, 9:08 PM

Quote:

Originally Posted by minijumbuk

Umm, I think it's only aqueous and gas.

thanks...i think thats what it is....can someone clarify this?

Undermyskin · 9 Oct 2008, 11:05 PM

It's correct, I think. I've never dealt with a K questions that have solid in it, to my ignorance, I suppose.

But revising what we need to do, I can prove it.

What we need to calculate K are the []s of chemicals involved. These can only be applied to aqueous solutions or gases only, right? Have you ever had a concentration of any solids? This is because the 'concentration' of a solid is preserved all the time. Taking a crystal of salt as an example. The number of molecules of NaCl/ the volume that crystal occupies = constant, yeah? Because even if adding more salt into an already concentrated solution, the extra settles to the bottom, joining the solid particles. And since the density of solid salt is the same at certain temperature and pressure, 'the concentration' is also the same. The more salt you add, the larger volume it occupies with the more molecules in there.

minijumbuk · 9 Oct 2008, 11:22 PM

Quote:

Originally Posted by Undermyskin

It's correct, I think. I've never dealt with a K questions that have solid in it, to my ignorance, I suppose.

But revising what we need to do, I can prove it.

What we need to calculate K are the []s of chemicals involved. These can only be applied to aqueous solutions or gases only, right? Have you ever had a concentration of any solids? This is because the 'concentration' of a solid is preserved all the time. Taking a crystal of salt as an example. The number of molecules of NaCl/ the volume that crystal occupies = constant, yeah? Because even if adding more salt into an already concentrated solution, the extra settles to the bottom, joining the solid particles. And since the density of solid salt is the same at certain temperature and pressure, 'the concentration' is also the same. The more salt you add, the larger volume it occupies with the more molecules in there.

2007 Industrial chemistry section. There was solid in the equilibrium. You just have to ignore it in the equilibrium expression.

tommykins · 9 Oct 2008, 11:28 PM

Solids are ignored, along with pure liquids (l)

Trebla · 9 Oct 2008, 11:54 PM

Quote:

Originally Posted by tommykins

Solids are ignored, along with pure liquids (l)

...because they have extremely high concentration which would make your K useless, if you included it.

tommykins · 10 Oct 2008, 12:14 AM

Quote:

Originally Posted by Trebla

...because they have extremely high concentration which would make your K useless, if you included it.

yeah i cbf'd writing out the reasoning. lol.

1 Oct 2008, 1:41 PM	#1 (permalink)
rparjf022 New Member HSC: 2008 Gender: Female Join Date: Oct 2007 Posts: 8 Last Activity: 16 Aug 2009, 1:16 AM	When calculating eq. constant... You can hide this advertisement by registering. When you calculate the equilibrium constant (K), do you need to put in units? Some people around me are saying yes and others no... so I'm pretty confused.

1 Oct 2008, 2:05 PM	#2 (permalink)
danz90 Supreme Member HSC: 2008 Gender: Male Location: Sydney Join Date: Feb 2007 Posts: 1,372 Last Activity: Today, 1:22 AM	Re: When calculating eq. constant... The equilibrium constant is only measuring the extent to which the forward reaction is occuring/favoured at particular conditions. If conditions such as pressure and temperature of the reaction are given, make sure you answer in this format: Kc = __ at T°C and ___kPa or ___atm For calculating, just sub in the equilibrium concentrations of the products and reactants into the equilibrium expression. Always round off to the lowest significant figure present in the question. __________________ 2008 NSW UAI: 98.20 BPharm @ USyd 2009

1 Oct 2008, 4:05 PM	#3 (permalink)
henry08 Exalted Member HSC: 2008 Gender: Male Join Date: Mar 2008 Posts: 861 Last Activity: 20 Nov 2009, 12:05 PM	Re: When calculating eq. constant... The syllabus dotpoint specifically states that no units are needed for equilibrium constant.

8 Oct 2008, 1:22 PM	#4 (permalink)
gezzill Junior Member HSC: 2008 Gender: Male Join Date: Nov 2007 Posts: 39 Last Activity: 29 Oct 2009, 10:18 PM	Re: When calculating eq. constant... mol/L i think, unless it specifically says.

8 Oct 2008, 1:26 PM	#5 (permalink)
minijumbuk ┗(^o^ )┓三 HSC: 2008 Gender: Male Join Date: Apr 2007 Posts: 654 Last Activity: 14 Jun 2009, 6:02 PM	Re: When calculating eq. constant... No units. __________________ "What's God?" "Well, you know... When you really want something, you'd close your eyes and wish for it... God's the guy who ignores you."

8 Oct 2008, 7:55 PM	#7 (permalink)
danz90 Supreme Member HSC: 2008 Gender: Male Location: Sydney Join Date: Feb 2007 Posts: 1,372 Last Activity: Today, 1:22 AM	Re: 回复: Re: When calculating eq. constant... There's no units for equilibrium constant... its just a figure that shows the extent to which the forward reaction in an equilibrium reaction is favoured, at a particular temperature. __________________ 2008 NSW UAI: 98.20 BPharm @ USyd 2009

9 Oct 2008, 8:43 PM	#8 (permalink)
cwag adonis HSC: N/A Gender: Male Join Date: Sep 2007 Posts: 132 Last Activity: 16 Nov 2009, 10:21 AM	Re: When calculating eq. constant... still on the same topic....iv seen many calculations in books where they don't seem to involve any solids or liquids in the K expression.....are they wrong. i thought it was plainly [products]/[reactants] no exceptions.? __________________ Year12 08 Adv English, Maths Ext1, Maths Ext2, Physics, Chemistry, Engineering Studies

9 Oct 2008, 8:49 PM	#9 (permalink)
minijumbuk ┗(^o^ )┓三 HSC: 2008 Gender: Male Join Date: Apr 2007 Posts: 654 Last Activity: 14 Jun 2009, 6:02 PM	Re: When calculating eq. constant... Umm, I think it's only aqueous and gas. __________________ "What's God?" "Well, you know... When you really want something, you'd close your eyes and wish for it... God's the guy who ignores you."

9 Oct 2008, 11:05 PM	#11 (permalink)
Undermyskin Self-delusive HSC: 2008 Gender: Male Join Date: Dec 2007 Posts: 598 Last Activity: 16 Jul 2009, 10:43 PM	Re: When calculating eq. constant... It's correct, I think. I've never dealt with a K questions that have solid in it, to my ignorance, I suppose. But revising what we need to do, I can prove it. What we need to calculate K are the []s of chemicals involved. These can only be applied to aqueous solutions or gases only, right? Have you ever had a concentration of any solids? This is because the 'concentration' of a solid is preserved all the time. Taking a crystal of salt as an example. The number of molecules of NaCl/ the volume that crystal occupies = constant, yeah? Because even if adding more salt into an already concentrated solution, the extra settles to the bottom, joining the solid particles. And since the density of solid salt is the same at certain temperature and pressure, 'the concentration' is also the same. The more salt you add, the larger volume it occupies with the more molecules in there. __________________ BPharmacy @ Usyd Class' 2013 When I was a child I caught a fleeting glimpse. Out of the corner of my eyes I turned to see but it was gone I cannot put my finger on it now The child is grown, the dream is gone... (Confortably numb - Pink Floyd)

9 Oct 2008, 11:28 PM	#13 (permalink)
tommykins i am number -e^i*pi HSC: 2008 Gender: Male Join Date: Feb 2007 Posts: 4,671 Last Activity: Today, 2:12 AM	回复: Re: When calculating eq. constant... Solids are ignored, along with pure liquids (l) __________________ \|3 C1\/1\|_ 3/\/G1/\/33\|21/\/G @ \|_\|/\/5\/\/ I

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