Does ΔT from evaportation increase or decrease with increasing molecular mass? Explain why?
The change in temperature (ΔT) during evaporation does not depend on the molecular mass of the substance undergoing evaporation. ΔT is primarily influenced by factors such as temperature, pressure, and the heat energy supplied to the substance.
To understand why the molecular mass does not affect ΔT during evaporation, let's examine the process of evaporation. Evaporation occurs when the molecules at the surface of a liquid obtain enough energy to escape into the surrounding space as vapor. During evaporation, the higher-energy molecules leave the liquid, reducing the average kinetic energy (temperature) of the remaining molecules, thus causing a cooling effect.
The molecular mass of a substance determines the average speed of its molecules at a given temperature. Heavier molecules move, on average, more slowly than lighter molecules. However, during evaporation, individual molecules escape based on their energy, not their mass. The molecules in a sample of liquid have a range of speeds and energies, and it is the higher-energy molecules that have sufficient energy to overcome the intermolecular forces and transition into vapor. As a result, evaporation occurs regardless of the molecular mass.
In summary, ΔT during evaporation is primarily determined by factors such as temperature, pressure, and the heat energy supplied to the substance. The molecular mass does not directly influence ΔT because individual molecules escape based on their energy, rather than their mass.