All you chemistry people, I need some help!

[FrogDog]

We're doing equilibrium in grade 12 HS chemisry right now, and I think my teacher may be teaching something incorrectly. When developing the equilibrium expression, which phases are not included? My notes say "pure liquids" and "pure solids" are not included. My teacher defined pure solids as any solid, and pure liquids as just the elemental liquids (Mercury and Bromine). So she says if there's an equation like this: CO (g) + H20 (l) <--> CO2 (g) + H2 (g) then you would include the H20 in your equilibrium expression. Her reasoning being that it's a "mixed" liquid because it's not just made up of one element like Br or H. She seems very unsure though.

Is this true or are you not supposed to include anything with an (l) after it?

Edit - Let me clarify I bit. I am talking about LeChatelier's Principle, and I am talking about the concentration of these elements and compounds when I refer to them.

 

[minendo]

I think you include gas and aq solutions.

 

[Mungla]

Are you talking about Le Chatelier's principle?

If so, then I've always been taught that you count gases. Keq=[products]/[reactants]. Equilibrium is just a balance between the reactants and the products. So, any gas reactant or product can influence the equilibrium. If you increase the concentration of a reactant, the reaction rate will increase for the forward reaction; so your equilibrium changes.

I may be wrong, as I'm only in HS Junior Chemistry.

When I come to think about it, we've always dealt with gases.. *tries to remember* We always left liquids and solids alone.

 

[Johnnie]

I read somewhere that glass is classified as a liquid..is that so?

 

[minendo]

Here is what it says in my Quantitative Chem text:


<< If one (or more) of the species is a pure liquid, a pure solid, or solvent in excess, no term for this species appears in the equilibrium constant expression. >>


Hope that helps.

 

[FrogDog]

<< Here is what it says in my Quantitative Chem text:


<< If one (or more) of the species is a pure liquid, a pure solid, or solvent in excess, no term for this species appears in the equilibrium constant expression. >>


Hope that helps. >>

The thing I don't know though is what defines a pure liquid (and pure solid as well for that matter).

 

[joohang]

Gosh.. I forgot my chem.

 

[nirgis]

Your teacher is wrong; any substance in liquid form is not included since its concentration does not change

edit: Having a multi-atom molecule does not change its solubility. NH3(l) for example is a pure substance. Now, if the substance dissociates and/or dissolves, that is an entire different story

 

[joohang]

<< I read somewhere that glass is classified as a liquid..is that so? >>


Yes. It is a supercooled liquid that flows extremely slowly.

 

[minendo]

<<

<< Here is what it says in my Quantitative Chem text:


<< If one (or more) of the species is a pure liquid, a pure solid, or solvent in excess, no term for this species appears in the equilibrium constant expression. >>


Hope that helps. >>

The thing I don't know though is what defines a pure liquid (and pure solid as well for that matter). >>


IF it is given as (l) or (s) I would leave it out. If it is given as (aq) or (g), then you use it.

 

[Heisenberg]

Aaaaaaaaaaaaahhhhhhhhhhhhhhhhhh!!!!!!!!!!!

Chemistry is the devil!!!!!!!!!!!!!!!!!!!!!!

*Runs away screaming*

 

[joohang]

<< Your teacher is wrong; any substance in liquid form is not included since its concentration does not change >>


What he said.

 

[FrogDog]

<< I think you include gas and aq solutions. >>

That would actually make sense. I think my teacher is wrong when she says to include "mixed" liquids. I think if something is specified in the equation as being liquid, then it doesn't get included. I don't know for sure though...

Edit - god I'm slow! What I jsut said was already said about 5 times.

Thanks guy, I think I've got it now.

 

[BMdoobieW]

Sorry dude. I've never told anyone this, and this doesn't leave this room, but I got a "D" in "Freshman Chemistry for engineers who are never going to use chemistry again 101." Then, to add insult to injury, three years later my sister joins me here and gets a "C" in the same class! Grrrrr. So I can't help you.

 

[Dudd]

Pure liquids and pure solids are not put into an equilibrium expression. How do you find a molarity to put in? You can't. H2O is never included. This is based on just doing this chapter in an AP class.

 

[vegetation]

H20 is not included in equilibrium expression.

 

[SubZeroX]

liquids (l) and solids (s) are not included in the equilibrium expression. Things such as gas (g) and aqueous solutions (aq) are included.

In the problem they usually just tell you whether it's liquid, solid, gas, or aqueous, so you don't actually need to determine whether they are pure or whatever. I think every problem I've done tells you exactly what they are.