{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

handout18

# handout18 - 5.4 Chemical Equilibrium In Mole Fractions and...

This preview shows pages 1–4. Sign up to view the full content.

5.4 Chemical Equilibrium In Mole Fractions and Molarity REMINDER: In section 4-14, we derived an expression for K P , the thermodynamic equilibrium constant, in terms of partial pressures (Eq. 4.210): K P = i " P eq i P 0 # ν i . (5.25) It is often more convenient to express this in terms of mole fractions or molarity, particularly when we are dealing with reactions in solution. AIM: Derive alternative expressions for the thermodynamic equilibrium constant. We will have partial pressures: K P mole fraction: K X fi molarity: K C Mole Fractions REMINDER: If we have a mixture of I different substances, consisting of n i moles of substance i , the mole fraction of species i is x i = n i I j = 1 n j . (5.26) The partial pressure of substance i is then P i = x i P and at 5–16

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
equilibrium we can write K P = i " P eq i P 0 # ν i (5.27) = i " x eq i P P 0 # ν i (5.28) = i h x eq i i ν i ! P P 0 i ν i (5.29) = K X P P 0 i ν i , (5.30) where x eq i is the mole fraction at equilibrium. Molarity REMINDER: Molarity is defined as c i = n i V = n i P nRT = P i RT . (5.31) We would like to work with a dimensionless quantity, which c i is not, so we introduce the ratio c i c 0 . Now we can express the partial pressure ratio as P i P 0 = RTc i P 0 (5.32) = c i c 0 c 0 RT P 0 . (5.33) 5–17
Then, at equilibrium we can write K P = i " P eq i P 0 # ν i (5.34) = i " c eq i c 0 c 0 RT P 0 # ν i (5.35) = i " c eq i c 0 # ν i ! c 0 RT P 0 i ν i (5.36) = K C c 0 RT P 0 i ν i . (5.37) REMINDER: Remember that K P is a dimensionless number. So are K X and K C . NOTE: In general, K P , K X and K C are all different for a given reaction.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}