Carbon monoxide is toxic because it binds more strongly to...

Carbon monoxide is toxic because it binds more strongly to iron in hemoglobin (Hb) than does $\mathrm{O}_{2} .$ Consider the following reactions and approximate standard free energy changes: $$\begin{aligned} \mathrm{Hb}+\mathrm{O}_{2} \longrightarrow \mathrm{HbO}_{2} & & \Delta G^{\circ} &=-70 \mathrm{kJ} \\ \mathrm{Hb}+\mathrm{CO} \longrightarrow & \mathrm{HbCO} & \Delta G^{\circ} &=-80 \mathrm{kJ} \end{aligned}$$ Using these data, estimate the equilibrium constant value at $25^{\circ} \mathrm{C}$ for the following reaction: $$\mathrm{HbO}_{2}+\mathrm{CO} \rightleftharpoons \mathrm{HbCO}+\mathrm{O}_{2}$$

Carbon monoxide is toxic because it binds more strongly to iron in hemoglobin (Hb) than does $\mathrm{O}_{2} .$ Consider the following reactions and approximate standard free energy changes:
$$\begin{aligned}
\mathrm{Hb}+\mathrm{O}_{2} \longrightarrow \mathrm{HbO}_{2} & & \Delta G^{\circ} &=-70 \mathrm{kJ} \\
\mathrm{Hb}+\mathrm{CO} \longrightarrow & \mathrm{HbCO} & \Delta G^{\circ} &=-80 \mathrm{kJ}
\end{aligned}$$
Using these data, estimate the equilibrium constant value at $25^{\circ} \mathrm{C}$ for the following reaction:
$$\mathrm{HbO}_{2}+\mathrm{CO} \rightleftharpoons \mathrm{HbCO}+\mathrm{O}_{2}$$

Key Concepts

Gibbs Free Energy

Gibbs free energy (?G°) is a thermodynamic potential that measures the maximum reversible work obtainable from a reaction at constant temperature and pressure. A negative standard free energy change indicates that the reaction is spontaneous under standard conditions, and it quantitatively links the energy landscape of the reaction to its equilibrium state.

Relationship Between ?G° and Equilibrium Constant

The equation ?G° = -RT ln K connects the standard free energy change of a reaction to its equilibrium constant (K). This relationship shows that a more negative ?G° corresponds to a larger equilibrium constant, meaning the reaction favors product formation. Here, R is the gas constant and T is the temperature in Kelvin.

Chemical Equilibrium

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products over time. Understanding the balance between forward and reverse reactions via the equilibrium constant is essential for predicting how changes in the system's conditions affect the position of equilibrium.

Ligand Binding Affinity

Ligand binding affinity describes how strongly a ligand binds to a specific binding site on a molecule, such as a protein. The differences in binding free energy for various ligands determine their relative affinities, which can have significant biological consequences, like the competitive inhibition observed in systems where multiple ligands vie for the same binding site.

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