Identify each energy exchange as primarily heat or work and determine whether the sign of ΔE is positive or negative for the system. a. Sweat evaporates from skin, cooling the skin. (The evaporating sweat is the system.)

Verified step by step guidance

1. Identify the type of process: Evaporation of sweat is an endothermic process, meaning the system (sweat) absorbs heat from the surroundings (skin).
2. Determine the type of energy exchange: Since the system absorbs heat, the primary energy exchange is heat.
3. Assess the direction of heat flow: Heat flows into the system (sweat) from the surroundings (skin), indicating that heat is absorbed by the system.
4. Determine the sign of ΔE (change in internal energy) for the system: When a system absorbs heat, the internal energy of the system increases, so ΔE is positive.
5. Conclude the energy exchange and sign of ΔE: The energy exchange is primarily heat, and the sign of ΔE for the system is positive.

Key Concepts

Energy Exchange

Energy exchange in thermodynamics refers to the transfer of energy between a system and its surroundings. This can occur in the form of heat, which is energy transferred due to temperature differences, or work, which is energy transferred when a force is applied over a distance. Understanding how energy is exchanged is crucial for analyzing changes in a system's internal energy.

Heat Transfer

Heat transfer is the process by which thermal energy moves from one object or system to another due to a temperature difference. In the context of the question, the evaporation of sweat from the skin represents a cooling effect, indicating that heat is leaving the system (the skin) to facilitate the phase change of sweat from liquid to vapor. This process is essential for regulating body temperature.

Change in Internal Energy (ΔE)

The change in internal energy (ΔE) of a system is defined as the total energy change resulting from heat and work interactions. According to the first law of thermodynamics, ΔE = q + w, where q is heat added to the system and w is work done on the system. In the case of evaporating sweat, heat is lost, leading to a negative ΔE for the system, indicating a decrease in internal energy.