Temperature and Gas

Looking for a Gas Gas is everywhere. There is something called the atmosphere. That's a big layer of gas that surrounds the Earth. Gases are random groups of atoms. In solids, atoms and molecules are compact and close together. Liquids have atoms that are spread out a little more. Gases are really spread out and the atoms and molecules are full of energy. They are bouncing around constantly. Gases can fill a container of any size or shape. It doesn't even matter how big the container is. The molecules still spread out to fill the whole space equally.

That is one of their physical characteristics. Think about a balloon. No matter what shape you make the balloon, it will be evenly filled with gas molecules. The molecules are spread equally throughout the entire balloon. Liquids can only fill the bottom of the container, while gases can fill it entirely. The shape of liquids is really dependent on the force of gravity, while gases are light enough to have a little more freedom to move. Compressing Gases Gases hold huge amounts of energy, and their molecules are spread out as much as possible.

With very little pressure, when compared to liquids and solids, those molecules can be compressed. It happens all of the time. Combinations of pressure and decreasing temperature force gases into tubes that we use every day. You might see compressed air in a spray bottle or feel the carbon dioxide rush out of a can of soda. Those are both examples of gas forced into a smaller space than it would want, and the gas escapes the first chance it gets. The gas molecules move from an area of high pressure to one of low pressure.

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What is the kinetic-molecular theory? The kinetic-molecular theory states: 1) All matter is composed of very small particles called atoms, ions, or molecules. 2) All of these small particles are in constant motion, even at the coldest temperature whether vibratory or translatory. 3)The kinetic energy of the particles is a measure of temperature. The greater the number of impacts the greater will be the pressure and vice-versa. 4) These particles collide but the total energy remains the same. Properties

The Link Between P and the pressure of gas results from collisions between the gas particles and the walls of the container. Each time a gas particle hits the wall, it exerts a force on the wall. An increase in the number of gas particles in the container increases the frequency of collisions with the walls and therefore the pressure of the gas. Amontons' Law (PT)The last postulate of the kinetic molecular theory states that the average kinetic energy of a gas particle depends only on the temperature of the gas.

Thus, the average kinetic energy of the gas particles increases as the gas becomes warmer. Because the mass of these particles is constant, their kinetic energy can only increase if the average velocity of the particles increases. The faster these particles are moving when they hit the wall, the greater the force they exert on the wall. Since the force per collision becomes larger as the temperature increases, the pressure of the gas must increase as well. Boyle's Law (P = 1/v)Gases can be compressed because most of the volume of a gas is empty space.

If we compress a gas without changing its temperature, the average kinetic energy of the gas particles stays the same. There is no change in the speed with which the particles move, but the container is smaller. Thus, the particles travel from one end of the container to the other in a shorter period of time. This means that they hit the walls more often. Any increase in the frequency of collisions with the walls must lead to an increase in the pressure of the gas. Thus, the pressure of gas becomes larger as the volume of the gas becomes smaller.

Charles' Law (V  T)The average kinetic energy of the particles in a gas is proportional to the temperature of the gas. Because the mass of these particles is constant, the particles must move faster as the gas becomes warmer. If they move faster, the particles will exert a greater force on the container each time they hit the walls, which leads to an increase in the pressure of the gas. If the walls of the container are flexible, it will expand until the pressure of the gas once more balances the pressure of the atmosphere.

The volume of the gas, therefore, becomes larger as the temperature of the gas increases. Avogadro's Hypothesis (V  N)As the number of gas particles increases, the frequency of collisions with the walls of the container must increase. This, in turn, leads to an increase in the pressure of the gas. Flexible containers, such as a balloon, will expand until the pressure of the gas inside the balloon once again balances the pressure of the gas outside. Thus, the volume of the gas is proportional to the number of gas particles. Dalton's Law of Partial Pressures (Pt = P1 + P2 + P3 + ... Imagine what would happen if six ball bearings of a different size were added to the molecular dynamics simulator. The total pressure would increase because there would be more collisions with the walls of the container. But the pressure due to the collisions between the original ball bearings and the walls of the container would remain the same. There is so much empty space in the container that each type of ball bearing hits the walls of the container as often in the mixture as it did when there was only one kind of ball bearing on the glass plate.

The total number of collisions with the wall in this mixture is therefore equal to the sum of the collisions that would occur when each size of ball bearing is present by itself. In other words, the total pressure of a mixture of gases is equal to the sum of the partial pressures of the individual gases. Graham's law of effusion can be demonstrated with the apparatus in the figure below. A thick-walled filter flask is evacuated with a vacuum pump. A syringe is filled with 25 mL of gas and the time required for the gas to escape through the syringe needle into the evacuated filter flask is measured with a stop watch.

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