4 O2(g) + Hb(aq) ⇌ [Hb(O2)4](aq)
• Kp → equilibrium units in terms of pressure of gaseous species
Pfetal = 0.025 atm
Kp, fetal = 2.56x106
Padult = 0.035 atm
Kp, adult = 6.44x105
Kp and Kc are related to one another by the following equation below:
R = gas constant = 0.08206 (L∙atm)/(mol∙K)
T = temperature, K
Δn = moles of gas products – moles of gas reactants
Δn = 0 moles gas – 4 moles gas
Δn = –4 mol
T = body temperature = 37°C + 273.15 = 310.15 K
The protein hemoglobin (Hb) transports O2 in mammalian blood. Each Hb can bind 4 O2 molecules. The equilibrium constant for the O2-binding reaction is higher in fetal hemoglobin than in adult hemoglobin. In discussing protein oxygen-binding capacity, biochemists use a measure called the P50 value, defined as the partial pressure of oxygen at which 50% of the protein is saturated. Fetal hemoglobin has a P50 value of 19 torr, and adult hemoglobin has a P50 value of 26.8 torr. Use these data to estimate how much larger Kc is for the aqueous reaction 4 O2(g) + Hb(aq) ⇌ [Hb(O2)4](aq) in a fetus, compared
to Kc for the same reaction in an adult.
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