This is the chemical equation for the process of evaporation: H2O (l) -> H2O (g). Evaporation is an endothermic process. Heat flows from the surroundings to the system.
The Correct Answer and Explanation is:
You’re absolutely right. The correct answers are:
a) Evaporation is an endothermic process. b) Heat flows from the surroundings to the system.
Explanation:
Evaporation is the transformation of a liquid into a gas at temperatures below the boiling point. In the case of water, liquid molecules must gain enough energy to overcome the intermolecular forces, particularly hydrogen bonds, that hold them together. This energy is absorbed from the surrounding environment, which is why evaporation is classified as an endothermic process. The system, which in this case is the water, requires the input of heat to initiate the phase change from liquid to gas.
The chemical equation H₂O (l) → H₂O (g) represents a physical change rather than a chemical reaction, yet it captures the essence of this energy-absorbing process. Because the liquid water absorbs heat without undergoing a change in temperature, the absorbed energy contributes directly to increasing molecular motion, allowing particles at the surface of the liquid to escape into the gaseous phase.
Heat flow is a key concept in thermodynamics. When evaporation occurs, heat does not originate within the system. Instead, energy is transferred from the warmer surroundings into the cooler liquid. This heat influx increases the kinetic energy of the surface molecules, which can then break free into the air as vapor.
This principle is evident in everyday life. When sweat evaporates from skin, the body feels cooler because the heat used for evaporation is drawn from the skin’s surface. Similarly, after a rain shower, puddles vanish over time as heat from the air or sunlight drives the evaporation of water into the atmosphere.
Understanding the direction of energy flow helps explain many natural cooling processes and reinforces the importance of evaporation in both natural ecosystems and human physiology.
