Problem 32 - Chemistry: An Atoms-Focused Approach

Question

Describe the difference between an internal energy change \((\Delta E)\) and an enthalpy change \((\Delta H)\).

Step-by-Step Solution

Answer

Answer: The key differences between internal energy change (ΔE) and enthalpy change (ΔH) are: 1. ΔE represents the change in total energy of a system considering all forms of energy, while ΔH takes into account only the change in internal energy along with the work done by or on the system due to pressure-volume change. 2. ΔH is a better measure of heat exchange in processes where pressure is constant, whereas ΔE is used for processes where there is no pressure-volume change or when the heat exchange is not of interest. 3. The relationship between ΔE and ΔH can be given by the equation: ΔH = ΔE + PΔV, showing that the difference between them is due to the amount of work done by or on the system in cases where there is no change in volume.

Step 1: Define internal energy change

Internal energy (\(E\)) is the total energy contained within a thermodynamic system. It consists of the kinetic energy of the particles, potential energy of the intermolecular forces, and any other forms of energy present in the system. The internal energy change, denoted as \(\Delta E\), is the difference in internal energy between the initial and final states of a process as a result of heat transfer and/or work being done on or by the system. Mathematically, it can be represented as \(\Delta E = E_{final} - E_{initial}\).

Step 2: Define enthalpy change

Enthalpy (\(H\)) is another thermodynamic property of a system, defined as the sum of its internal energy and the product of its pressure (\(P\)) and volume (\(V\)). Mathematically, it can be represented as \(H = E + PV\). The enthalpy change, denoted as \(\Delta H\), represents the difference in enthalpy between the initial and final states of a process, and it is often used to measure the heat exchange at constant pressure. Mathematically, it can be represented as \(\Delta H = H_{final} - H_{initial}\).

Step 3: Describe the differences between internal energy change and enthalpy change

The key differences between internal energy change (\(\Delta E\)) and enthalpy change (\(\Delta H\)) can be summarized as follows: 1. \(\Delta E\) represents the change in total energy of a system considering all forms of energy, while \(\Delta H\) takes into account only the change in internal energy along with the work done by or on the system due to the pressure-volume change. 2. In processes where pressure is constant (such as most chemical reactions), the enthalpy change (\(\Delta H\)) is a better measure of heat exchange as it accounts for the work done by the system due to volume change. In contrast, the internal energy change (\(\Delta E\)) is used for processes where there is no pressure-volume change or when the heat exchange is not of interest. 3. The relationship between these two properties can be given by the equation: \(\Delta H = \Delta E + P\Delta V\). This equation shows that in cases where there is no change in volume, the difference between the internal energy change and the enthalpy change is due to the amount of work done by or on the system.