Chemistry stuff

[Foobarz]

If anyone could explain to this high school going to be a sophomore (I'm preparing for AP Chem):

Why does temperature affect the value of an equilibrium constant (Kc) but pressure does not? Don't both types of stress change the concentration of the products or reactants (but not both products and reactants equally), thus changing Kc?

If you can help me, thank you very much!

PS: I hope that anything can be asked in the community cafe.

[jerenept]

If anyone could explain to this high school going to be a sophomore (I'm preparing for AP Chem):

Why does temperature affect the value of an equilibrium constant (Kc) but pressure does not? Don't both types of stress change the concentration of the products or reactants (but not both products and reactants equally), thus changing Kc?

If you can help me, thank you very much!

PS: I hope that anything can be asked in the community cafe.

http://en.wikipedia.org/wiki/Equilibrium_constant ?

[dh04000]

If anyone could explain to this high school going to be a sophomore (I'm preparing for AP Chem):

Why does temperature affect the value of an equilibrium constant (Kc) but pressure does not? Don't both types of stress change the concentration of the products or reactants (but not both products and reactants equally), thus changing Kc?

If you can help me, thank you very much!

PS: I hope that anything can be asked in the community cafe.

Ah! That's a good question, and it all comes down to Thermodynamics!

The simple explanation is that while pressure can affect a reaction, such as extremely high pressures stopping a reaction that would have released a gas, pressure does not change the equilibrium of a reaction, just the rate at which it occurs. Temperature on the other hand can change the equilibrium of a reaction due being "part" of the reaction. You know that adding more reactant can cause a solution at Eq to shift, creating more product. Adding more product will shift the reaction back to reactant. Temp. is part of this due to Energy being part of the reaction. If a reaction is exothermic, as in heat releasing, then the reaction is as following:

A + B = C + D + heat

Changing the temperature of the reaction, such as 20 Celsius to 100 Celsius would add more energy, or heat to the right side, thus shifting the equilibrium towards the reactant, just as adding more product would.

Pressure is not a form of energy, just a state condition, thus not part of the reaction, or equilibrium.

If you have any questions, or I confused you, feel free to ask.


-PhD Candidate in Biochemistry