Physics

Van der Walls is the name of a Dutch physicist, J. D. van der Waals (1837-1923). The Van der Waals Equation of State is an equation of state of a gas, similar to The equation of state of an ideal gas. The difference is, The equation of state of an ideal gas cannot provide accurate results if the pressure and density of real gas are large enough. Whereas The Van der Waals Equation of State can produce more accurate results.

The existence of this equation originated from Van der Waals, who realized the limitations of the equation of state of an ideal. Waals, modify the equation of state of the ideal gas, by adding several factors that also influence the real gas condition, when the pressure and density of the real gas are large.

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The evaporation process can be explained using kinetic theory. Like gas molecules, water molecules also move. The difference is that water molecules cannot be scattered because the attraction between molecules can still hold them together. Conversely, the attraction between the gas molecules is fragile, so that the gas molecules cannot fuse. When moving, water molecules have velocity. There are water molecules that have high speeds; there are also water molecules that have a small velocity. The distribution of the velocity of the water molecule resembles the Maxwell distribution.

Evaporation occurs when the speed of the water molecule is large enough so that the attraction between the water molecules is unable to hold it together. Similar to rockets moving into space, the speed of a rocket is large enough so that the gravitational force of the earth cannot hold it to stay on earth. Note that only molecules with large velocities can escape from the attraction between molecules. The molecules with small speeds remain together like water.

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Boiling is a process of changing liquid into gas. Boiling occurs when the saturated vapor pressure is equal to the air pressure (air pressure = atmospheric pressure). We only discuss boiling water. The saturated vapor pressure of water is directly proportional to the temperature of the water, the higher the water temperature, the higher the pressure of saturated vapor. When we heat water, small bubbles usually appear on the bottom of the container. The existence of bubbles indicates the change in a liquid into a gas. If the saturated vapor pressure in the bubble is smaller than the outside air pressure, the bubble will shrink and disintegrate before arriving at the surface. Bubbles are destroyed because the thrust force of the outer air is higher than the thrust force of the steam inside the bubble. The external air pressure is higher than the vapor pressure in the bubble so that the outside air has a more significant force (P = F / A).

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Humidity states the amount of water vapor in the air. When it rains, the atmosphere is very humid because there is a lot of water vapor in the air. Conversely, if the water vapor in the air is very little, the air is arid. The amount of water vapor in the air is expressed by the relative humidity.

The relative humidity is the ratio of the partial pressure of steam to the pressure of saturated vapor of water at a certain temperature (steam is water vapor). Relative humidity is expressed in percent, mathematically formulated:

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If we look carefully, the smoke from the combustion initially can be seen. After a while, smoke cannot be viewed. Have you used a perfume? Even though you spray perfume in the room, other people who are outside the home can also feel the fragrance of the perfume. Likewise, if the mother cooks delicious and appetizing food in the kitchen, the aroma of cooking can be felt from a neighbor’s house. Why is that?

There are many other examples. If you put a few drops of ink into a glass containing clear water, ink, or food coloring will spread evenly throughout the water. This happens automatically. Some previous examples are diffusion events that are often experienced in everyday life. Diffusion is the process of moving substances from a high concentration to a low concentration. What is meant by concentration is the number of molecules/moles of a substance per volume. A high concentration place is a place where there are many molecules of substances per volume. Conversely, low concentrations are places where there are few molecules per volume.

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Energy in a monatomic ideal gas

The energy in the monatomic ideal gas is the total amount of translational kinetic energy of monatomic ideal gas molecules. The total amount of translational kinetic energy of the ideal gas molecules = the product of the average translational kinetic energy of each molecule and the number of molecules (N). Mathematically:

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The energy equipartition theorem was derived theoretically by Clerk Maxwell using statistical mechanics. It is called a theorem because there is no proof through experimentation. The energy partition means equal distribution of energy.

KE = average translational kinetic energy of gas molecules (Joule)

k = Boltzmann’s constant = 1.38 x 10^-23 J/K

T = absolute temperature of the ideal gas molecule (Kelvin)

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In addition to pressure, one of the quantities that states the macroscopic nature of gas is temperature (T). Gas pressure equation:

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The kinetic theory states that every substance consists of atoms or molecules and that the atom or molecule moves continuously carelessly. This assumption of kinetic theory matches the situation and condition of the atom or molecule of the gas constituent. The force of attraction between the atoms or molecules making up the gas is feeble so that atoms or molecules can move freely.

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Article Boyle’s law, Charles’s law, Gay-Lussac’s law

Boyle’s law

Robert Boyle (1627-1691) conducted experiments to investigate the quantitative relationship between gas pressure and volume. This experiment is carried out by inserting a certain amount of gas into a closed container. Until a pretty good approach, he found that if the gas temperature was kept constant, then when the gas pressure increased, the gas volume was reduced. Likewise, when the gas pressure decreases, the gas volume increases. Gas pressure is inversely proportional to gas volume. This relationship is known as Boyle’s Law. Mathematically:

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