Problem 135 - Chemistry An Atoms First Approach

Question

When heat is added to proteins, the hydrogen bonding in the secondary structure is disrupted. What are the algebraic signs of \(\Delta H\) and \(\Delta S\) for the denaturation process?

Step-by-Step Solution

Answer

For the denaturation process of proteins when heat is added, the algebraic signs of ΔH and ΔS are both positive: \( \Delta H > 0 \) and \( \Delta S > 0 \). This is because energy is absorbed to break hydrogen bonds (leading to a positive ΔH), and the protein's structure becomes more disordered (leading to a positive ΔS).

Step 1: Understanding the denaturation process

When heat is added to proteins, the hydrogen bonds that stabilize the secondary structure are disrupted. This process is called denaturation. As a result, the protein loses its specific folded structure and becomes a random coil.

Step 2: Analyze the change in enthalpy (ΔH) during denaturation

Enthalpy (H) is the measure of the total energy of a system, which includes the internal energy and the energy associated with any external effects (like pressure and volume changes). When denaturation occurs, the hydrogen bonds within the protein are broken, which requires energy to be absorbed by the system. Therefore, the change in enthalpy, ΔH, during the denaturation process will be positive, as heat is added to break the hydrogen bonds.

Step 3: Analyze the change in entropy (ΔS) during denaturation

Entropy (S) is a measure of the degree of disorder or randomness of a system. During denaturation, the protein changes from a specific folded structure to a disordered random coil. As a consequence, the degree of disorder increases, leading to an increase in entropy. Thus, the change in entropy, ΔS, during the denaturation process will be positive In conclusion, for the denaturation process when heat is added to proteins, we get:

Step 4: Algebraic signs of ΔH and ΔS

For denaturation of proteins, the algebraic signs of ΔH and ΔS are as follows: ΔH > 0 (positive) ΔS > 0 (positive)