University:
University of Alberta
Course:
CHEM 101 | Introductory University Chemistry I
Academic year:

2024
Views:

466

Pages:

4
Author:

Neena N.

Kinetic Molecular Theory Gases are produced in a range of reactions, including combustion reactions. It is important to understand the properties and behaviour of these gases. Gases have a much lower density than liquids or solids. They will always expand to fill the available space because the particles have very little interaction with one another. The gases can be compressed very easily (resulting in increased pressure) and will rapidly mix together with other gases. Kinetic Molecular Theory Kinetic molecular theory is a model to explain gas behaviour. There are some key points to this theory: ● Gases are composed of small particles (atoms or particles). ● Gases will occupy as much space as they can and have low density. This means there is a lot of empty space between gas particles. ● Gas particles move in straight lines, but in random directions. ● Particles will collide with each other and the wall of the container. ● The forces between as particles are extremely weak. ● The kinetic energy (movement) can be transferred between particles, but the total energy is not lost. This is known as elastic collisions. ● The average kinetic energy of gas particles increases as temperature increases. This theory is used to describe the behaviour of gases. Pressure Gases will always fill the entire space available. The amount of force that is exerted on the walls of the container by the gases is the pressure. As gases are compressed, the frequency of collisions between gas particles and the container wall will increase. Therefore, pressure is described by force per unit area. When there is more than 1 gas, the process is the same. For a mixture of oxygen and nitrogen at constant temperature, the oxygen will collide with the walls of the container exerting a pressure. The nitrogen will also collide with the walls of the container exerting a pressure. The measured pressure is the sum of the partial pressure of the oxygen and the partial pressure of the nitrogen. In other words, partial pressures are additive. Units of Pressure As we said before, pressure is measured by force over unit area. The units of pressure depend on the units to measure both force and area. There are many possible units to measure pressure which can get confusing. The Sl unit for pressure is Newtons per square meter (N m¯²). One Newton per square meter is 2 equivalent to a pressure of 1 Pascal (Pa). Pressure can also be measured in bar, where 1 bar is equal to 100 kilopascal (kPa). Mercury barometers are an older way to measure pressure which use the units millimetres of mercury (mmHg). Another unit for measuring pressure is the standard atmosphere (atm). 1 atm is equivalent to 760 mmHg (at 25 °C) and also 101.3 kPa. Overall, the most common units of pressure are: 1. pascal 2. bar 3. mmHg 4. atm. Converting Units of Pressure The following table outlines the conversion between the most common units. Worked Example Convert 0.437 atm into kPa and also bar. Answer 1. To convert 0.437 atm into kPa, use the conversion 1 atm = 101.3 kPa. = 0.437 x 101.3 = 44.3 kPa 2. To convert 0.437 atm into bar, convert to kPa and then convert to bar. We already know 0.437 atm = 44.3 kPa. Use the conversion 1 bar = 100 kPa. = 44.3 / 100 = 0.443 bar