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Flashcards in Gases Equilibrium add-in Deck (5)
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1
Define:

Kc, the molar concentration equilibrium constant

Kc is the value of Keq when all reactant and product concentrations are given in concentration units, such as mol/l.

When reactant and product concentrations are given in these units, Kc will be the calculated value of equilibrium.

2
Define:

Kp, the partial pressure equilibrium constant

Kp is the value of Keq when all reactant and product concentrations are given in pressure units, such as atm.

When reactant and product concentrations are given in these units, Kp will be the calculated value of equilibrium.

3

How can the value of Kp be calculated, given the value of Kc?

The equation relating Kp to Kc is:

Kp = Kc (RT)Δn

where:

R = the ideal gas constant in l-atm/K-mol
T = the absolute temperature in K
Δn = the change in moles of gas (moles product gas - moles reactant gas)

4

At STP, if the number of moles of gas decreases significantly in a reaction, what will be the relationship between Kp and Kc?

Kc will be greater than Kp.

The equation relating Kp to Kc is:

Kp = Kc (RT)Δn

Since at STP, R*T is greater than 1, and since Δn is negative if number of moles of gas decreases, this gives :

Kp = Kc (1 / [number greater than 1]), hence Kp is a fraction of the size of Kc.

5

At STP, if the number of moles of gas remains the same in a reaction, what will be the relationship between Kp and Kc?

Kc will be equal to Kp.

The equation relating Kp to Kc is:

Kp = Kc (RT)Δn

If the number of moles of gas is unchanged, Δn must equal zero, this gives:

Kp = Kc ([RT]0)=Kc * 1,
hence Kp = Kc.