Question

Identify the phases of eg. (l),(s),(g),(aq) : 4KI2 + Cl2 ---> 2K2Cl + 2I2.....please help me i do not knowhow to tell the phases of each one...

Answer 1

KI is a solid (most ionic compounds are at room temperature) while Cl2 is a gas (think HOFBrINCl). However, since they're undergoing a chemical reaction, I would probably say KI is dissolved in water (state would be aqueous), otherwise the reaction would proceed too slowly. This means the KCl (not K2Cl as written above) would also be aqueous. I2 is also a gas.

Summary: KI (aq), Cl2 (g), KCl (aq), I2 (g)

Answer 2

Well, first, these are very strange compounds, and I wonder whether you have made a typo or some other mistake in writing the equation down in the first place. K is a Group 1A metal, and forms the ionic compounds KI with iodine and KCl with chlorine. I've never heard of KI2 nor K2Cl. These look very much like mistakes.

If we interpret your equation as 2 KI + Cl2 -> 2 KCl + I2, then there are two possibilities. As matt noted, KI and KCl are water-soluble ionic substances, and are essentially always found, in ordinary lab situations, as either solids or dissolved. Cl2 in its standard state, near 1 atm pressure and room temperature, is a gas, and I2 is a solid.

So one possibility is that you have this reaction:

2 KI(s) + Cl2(g) -> 2 KCl(s) + I2(s)

That would consist of chlorine gas reacting with KI solid, producing KCl solid and solid I2. It would indeed generally proceed slowly, because it relies on the Cl2 chipping away at the KI surface. But the KCl and I2 formed would tend to block additional access to the surface, once the reaction went a little bit. It would work if the solid were finely powdered or something, though...

Another possibility is that all the reactants are dissolved. One wrinkle here is that the KCl and KI would then be present as their ions, not the complete solids, so that in principle your equation should read:

2 I-(aq) + Cl2(aq) -> 2 Cl-(aq) + I2(aq)

Or possibly, if, say, the gas were being bubbled into the solution, and the I2 were precipitating out:

2 I-(aq) + Cl2(g) -> 2 Cl-(aq) + I2(s)

Personally I suspect the first answer is the one you want, because you're probably be asked to identify the standard states (states at 1 atm pressure and room tmperature) of the elements and compounds in the reaction. You're expected to know that Cl2 is a gas under those conditions, I2 is a solid, and both KI and KCl are solids.