The reaction shown below occurs in the blood between hemoglobin (Hb) and oxygen.

Hb + O2 ⇄ HbO2

Which of the following correctly describes this reaction:

A. equilibrium reaction

B. in the lungs, the reaction proceeds to the right

C. in the muscles, the reaction proceeds to the left

D. The K value for the reaction is extremely small.

A and D only

B and C only

A, B, and C only

A, B, C, and D

A, B, C

Explanation:

Notice that this reaction involves double arrows, meaning this represents an equilibrium reaction in which we observe a forward reaction (combination of hemoglobin and oxygen) and a reverse reaction (decomposition of the oxyhemoglobin complex).

Upon inhalation of oxygen, it accesses the blood of a person and binds to hemoglobin, so the following reaction proceeds to the right.

Similarly, the opposite process takes place in muscles, oxyhemoglobin is decomposed back into hemoglobin and oxygen.

The equilibrium constant reaction is relatively high, since at standard conditions, this is a spontaneous reaction, hemoglobin combines with oxygen without any additional external source of energy.