Changes Of Matter State To define matter, one would say that it is something that occupies space and has weight. Matter naturally occurs in three phases: solid, liquid, and gas. Changing from a solid to a liquid, liquid to gas, etc. can be referred to as a change of state. Changes of state (or phase) effect our everyday lives.
This chapter on changes of phase should actually be called Energy Transfer. The whole basis on changing a substance’s state is that it is using energy to get from one state to another. To understand the “real” difference in the phases of matter, you must understand the difference in the energy of the phases. Energy is found inside matter. You can think of this energy as the motion of the particles making up the matter.
As the energy increases inside matter, the particles move faster and faster. Phase changes are a type of physical change. They require energy (in this case heat energy) to either be removed or added on to the substance. On earth, three main types of phases. These are: solids, liquids, and gases. The fourth phase is called plasma and the fifth which scientist are researching and building models of is super-solids.
The solid state is when a substance’s inner particles are not free to move around, but can vibrate. The liquid state is when a substance’s inner particles become a bit loose, and they are free to move around. They aren’t completely free, but have the ability to take the volume/shape of their container. In the gas state, the particles are free to move, and can take the form of and fill the container they are put in. Evaporation is the gradual change of a liquid to a gas without boiling. The factors that influence evaporation are temperature, solar energy/sunlight, low humidity, or saturation level or the air.
The temperature simply represents the average kinetic energy of the molecules in a substance. Molecules are constantly in motion, whether their speeds are fast or slow; they are never standing still. Their speeds mainly are dependent on the temperature of the liquid. At rapid speeds, (and high temperature) the molecules tend to “bump” each other, due to the molecular forces that are acting upon them. While “bumping” into each other, kinetic energy is either being gained or lost.
Those molecules that have gained kinetic energy are being pushed up from below, and this is the point where it may be possible for them to escape the surface of the liquid. In addition, they have to overcome the attractive forces pushing them downward. Because few molecules are able to attain this status, few escape. This is the main reason why evaporation of a liquid is such a slow process, and it also explains why evaporation is referred to as a “cooling process”. Such is used even in the human body, where sweat glands cause a heated body to perspire to maintain body temperature.
The molecules that are not able to escape the surface are left in the liquid, therefore cooling the liquid because the molecules contain a lower velocity (they aren’t moving as fast). Amazingly enough, there is a process that reverses the effect of evaporation. This is called condensation, which is when a gas changes to a liquid. Condensation is a cooling process. Taking away the heat shrinks the volume of the vapor and lowers the velocity of the molecules, plus the distance between them.
The loss of energy will cause the transformation of the gas into a liquid. Basically, there are molecules in the air that want to become a liquid, and the opposite of evaporation occurs. They are attracted to the liquid, and once they get close enough to it, or get enough kinetic energy to get near it, they may strike it. At this point, the molecule has just slammed into other molecules and it has lost it’s kinetic energy. Now, even if it wanted to escape, it would have to gain way too much energy. So it is stuck in the liquid, and is now a part of it. There are always different levels of water vapor in the air.
The relative humidity compares the temperature with how much water is in the air. When the air is holding as much vapor as it can, the most before it turns into a liquid, it is referred to as being saturated, or at 100% humidity. This also happens when there is an equilibrium (an equal amount of water molecules are being evaporated and condensed). This ultimately happens when the slower molecules in the air tend to “stick” to each other and form a liquid-like vapor in the air. It can occur in low or high temperatures. In this same case, if the larger particles condense, it has just made a cloud or fog.
Fog is the same thing as a cloud, except fog occurs near the surface of the earth while a cloud occurs in higher elevation. They form when air cools and is unable to contain as much water vapor. The condensation and cooling of the air causes them to happen . So what happens if there gets to be too much water vapor, that the air can’t hold it all? The droplets would stick to each other and cause what we know as rain. * Evaporation and condensation are relatively slow processes.
This is due to the fact that it takes a lot of energy for just one molecule to escape the state that it’s in to become another . Different situations make substances evaporate and condense at varying rates. So if you leave a glass of water out for a few days and the water level doesn’t change, does that mean that evaporation and condensation didn’t occur? Not at all! What has occurred is called an equilibrium. This happens when the liquid evaporates and condenses at the same rate. If the air doesn’t contain much water, evaporation will occur a lot quicker than condensation will.
In air where there is a lot of water, evaporation will happen only a little faster than condensation. On dry summer days it is possible to stay reasonably comfortable even though the temperature is fairly hot . The reason is that our bodies perspire, cooling us off. We may not even know that we are perspiring because it evaporates so fast off of the skin that we don’t even notice. On the other hand, on humid days the evaporation rate is so slow that we constantly feel sticky and wet.
Water vapor in the air effects the evaporation and condensation rates. Water boils at 100* Celsius, and despite popular belief it is actually a cooling process. Water is being cooled by boiling as fast as it is being heated by energy from the heat source. When the heat source warms the pot of water, the heat turns the water closest to it into a gas. The gas molecules are, at this point, moving faster than that of the liquid. The gas will want to get to the surface of the liquid so it can escape, and it will push it’s way through the liquid to get to the surface.
This is why boiling water bubbles! One major factor of boiling water is that it all depends on the atmospheric pressure. An example of the role that pressure has on the boiling point would be found at sea level. Boiling point would be at about 97* C rather than 100* C, because the vapor pressure cannot exceed the atmospheric pressure . In addition, if water is already boiling, it will remain at a constant temperature. Even if more and more heat is added, it will not fluctuate it’s temperature. The Gas Laws: Boyle’s Law – The volume of a fixed amount of gas varies inversely with the pressure of the gas.
As pressure increases, volume decreases. As pressure decreases, volume increases. Charles’ Law – The volume of a fixed amount of gas varies directly with the temperature of the gas. As temperature increases, volume increases. As temperature decreases, volume decreases.