What is Delta S and Delta H?

Enthalpy (H):

Enthalpy is the sum of a system’s internal energy (E) and the product of its pressure (P) and volume (V). It is a state function, meaning its value depends only on the current state of the system, not on how it got there. Enthalpy is measured in calories, joules, or BTUs.

Mathematically:

H=E+PV<

In a chemical reaction under constant pressure, the change in enthalpy (ΔH) represents the difference between the energy required to break bonds and the energy released when new bonds form. Simply put, ΔH tells us how much heat is absorbed or released during a process.

• ΔH > 0: The system absorbs energy (endothermic process).
• ΔH < 0: The system releases energy (exothermic process).

Entropy (S):

Entropy measures the degree of disorder or randomness in a system. It is the amount of thermal energy per unit temperature that cannot be used to perform useful work. The SI unit of entropy is joules per Kelvin (J/K), and changes in entropy are represented as ΔS.

• ΔS > 0: Entropy increases, meaning the system becomes more disordered.
• ΔS < 0: Entropy decreases, meaning the system becomes more ordered.

In summary, enthalpy tracks the total energy change during a process, while entropy indicates the level of disorder in the system. Both are key concepts in understanding the thermodynamics of chemical reactions.