During an energy exchange, a chemical system absorbs energy from its surroundings. What is the sign of \(\Delta E_{\text {sys }}\) for this process? Explain.

When discussing chemical systems, 'internal energy' is a key term, referring to the total energy contained within a system. It encompasses all forms of energy present, including kinetic energies of the molecules, potential energies between the molecules, and, in the case of chemical reactions, the chemical potential energies within the bonds of the substances involved.

According to the laws of thermodynamics, the internal energy of an isolated system remains constant. However, in other systems, such as those in a chemical laboratory, energy can be exchanged with the surroundings. For example, during a reaction, when a chemical system absorbs energy, this is seen as a gain in the internal energy, which is denoted as a positive change in internal energy, or \( \Delta E_{\text{sys}} > 0 \). This positive sign is symbolic in thermodynamics, indicating that the energy of the system has increased.

Energy absorption is a phenomenon where a system takes in energy from its environment. This can occur in various forms, such as heat being absorbed during an endothermic reaction or light energy being harnessed during photosynthesis in plants.

In the context of chemical reactions, when a substance absorbs energy, it often results in molecular excitation leading to reactions or phase changes. For instance, absorbing heat can cause ice to melt or water to boil. The ability of a system to absorb energy directly impacts its internal energy. It is important to distinguish between different types of energy absorption, and in a chemical context, it frequently involves heat (\( q \) is often used to symbolize heat in equations). Therefore, during energy absorption, \( q > 0 \), indicating that energy is being transferred to the system from the surroundings.

Thermodynamics is the study of heat, work, and the associated energy exchanges. Central to this field are the laws of thermodynamics, which govern the principles of energy transfer within and between systems.

The first law, also known as the law of energy conservation, informs us that energy cannot be created or destroyed, only transferred or converted from one form to another. In the scenario of a chemical system absorbing energy from its surroundings, thermodynamics illuminate the process by which the system's internal energy changes.

For students grappling with these concepts, visualizing energy flow diagrams and understanding endothermic versus exothermic processes can greatly aid in understanding thermodynamics. Through graphs and diagrams, we can see how energy enters or exits a system during a reaction, which aligns with the signs of \( \Delta E_{\text{sys}} \) – positive for energy entering (absorption) and negative for energy leaving (release).