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Kinetic Molecular Theory
Kinetic Molecular Theory
[MELC 21] Investigate the relationship between: 1. volume and pressure at a constant temperature of a gas. 2. volume and temperature at a constant pressure of gas; and 3. explain these relationships using the kinetic molecular theory. (S9MT-IIj-20)
Day 1-2: Cite and describe each Kinetic Molecular Theory assumption and cite instances wherein KMT is observed in life experiences.
The kinetic-molecular theory explains the states of matter by positing that matter consists of tiny particles in constant motion. This theory aids in understanding the observable properties and behaviors of solids, liquids, and gases. Although it is most easily grasped in relation to gases, our detailed study will focus specifically on gases. The theory is particularly applicable to an ideal gas, a hypothetical model that perfectly conforms to all the assumptions of the kinetic-molecular theory. While real gases are not ideal, they closely resemble ideal behavior under most normal conditions. [©]
The Kinetic Molecular Theory (KMT) provides a molecular-level interpretation of the macroscopic properties of gases. Here are the main assumptions of KMT along with examples of where they can be observed in everyday life: [©]
These particles move in a straight line until they collide with another particle or the walls of the container.
Example: A balloon. The air molecules inside the balloon move in straight lines until they hit the inner walls of the balloon or other molecules, causing the balloon to expand.
These particles are much smaller than the distance between particles. Most of the volume of a gas is therefore empty space.
Example: Helium balloons. Helium atoms are very small and the distance between them is much greater than their size, which is why a helium balloon is light and can float in air.
There is no force of attraction between gas particles or between the particles and the walls of the container.
Example: A football inflated with air. The air particles inside the football do not stick to each other or to the inside of the ball, allowing the air to be evenly distributed throughout the volume of the ball.
Collisions between gas particles or collisions with the walls of the container are perfectly elastic. None of the energy of a gas particle is lost when it collides with another particle or with the walls of the container.
Example: Ping-pong balls in a closed container. When shaken, the balls bounce off each other and the walls of the container without losing energy, analogous to gas particles in a closed container
The average kinetic energy of a collection of gas particles depends on the temperature of the gas and nothing else.
Example: Heating a pot of water. As the water heats up, the kinetic energy of the water vapor (gas) molecules increases, causing them to move faster. This is why steam rises rapidly from boiling water.
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