The process of boiling is when a liquid becomes so hot that it vaporizes, changing from the liquid state to the gaseous state. The normal boiling point for many liquids and gases is 100°C. When looking at the entropy change when a liquid boils at its normal boiling point, there are two different scenarios: if enthalpy decreases with temperature (enthalpy changes by being released), then entropy will decrease; if enthalpy increases with temperature (enthalpy changes by absorbing heat), then entropy will increase. For example, when water boils at 100 °C, it has an increased enthalpy because it absorbs energy from its surroundings in order to vaporize into steam. Therefore, when water boils at its normal boiling point, entropy increases.
The average kinetic energy of gas molecules directly affects the temperature and pressure at which a substance will boil. The more energetic gas molecules are when they collide with one another, the higher their chances of overcoming inter-molecular attractions and escape as vapor from the liquid phase. However, an increase in entropy results from this process because it is less probable that all of these fast-moving molecules have enough time to attain equilibrium before escaping into the atmosphere as vapor. What’s happening here is that there is a change in the physical state–the particles go from being bound to each other (in liquid) to completely free (as gasses). Now imagine if you could take two identical containers filled with water: one container has lots of microscopic air bubbles mixed throughout the water, while the other container is completely filled with liquid. If you heat up both containers and wait for them to reach boiling point, the temperature would be higher in the first container because it takes more energy (heat) to boil bubbles of air than normal molecules of water.
After researching this question, it is clear that when br(l) boils at its normal boiling point, the entropy of a liquid decreases as the temperature increases.
The reason for this statement is because when heat energy starts to be added to the system there is an increase in disorder which corresponds with lower entropy than what was present before heating up the substance. The law states that if there are any changes or additions then some will have more disorder and some less so they balance out while remaining close enough together, to sum up to zero. When adding heat into a substance, molecules move faster which causes them scatter farther apart from each other due to being bombarded by more and thus becoming generally disordered. This leads us back to our original statement that when a substance boils, the entropy decreases.
The second law of thermodynamics states that as entropy increases with an increase in temperature and disorder within a system then it will decrease over time. The first law of thermodynamics is also considered to be consistent with this idea because energy cannot be created or destroyed but can only change from one form into another which leads us back to our original question concerning if adding heat would cause any changes on the actual boiling point. When considering increasing the quantity of heat added to a liquid at its normal boiling point there may not seem like anything has changed about it yet we must consider how much more disordered each molecule inside has become due to getting bombarded by so much excess energy compared to what was originally there.
The system has increased in entropy because of the heat and so when it boils at its normal boiling point, does its entropy increase or decrease? The answer to this question is that the total amount of disorder within a system will always remain constant over time no matter what type of changes happen as long as they are irreversible which leads us back to our original idea about if adding more heat would make any difference on the actual boiling point: there won’t be an effect until all molecules inside have been bombarded by enough energy for them to move around faster causing them to escape from their liquid form into becoming gas.
The heat that is added does not actually act on the molecules themselves but rather it increases the kinetic energy of those within, which then leads to an increase in entropy because there are more ways for these particles to be moving around without having any order.
