CHEM MODULE 3 Gas Laws

Gas Laws Gases are often formed as a product of or are used as a reactant in a chemical reaction. These materials (gases) have some special properties and are subject to some special calculations in chemistry. Gases (think of air as an example) are very light, are easily expandable, are easily compressible, and completely fill a container into which they are released. These properties are due to the fact that the individual molecules of the gas are very far apart from one another, are not attracted to one another and are in constant, very rapid motion. This description of gases is known as the kinetic-molecular theory of gases. Due to these properties, the volume of a sample of gas will expand (increase) if the temperature of the gas sample is increased and the volume of a sample of gas will contract (decrease) if the temperature of the gas sample is decreased. [The temperature scale used with gases is the Kelvin (K) scale, which is °C + 273]. [The volume scale used with gases is the liter scale, which is ml/1000]. Also, the volume of a sample of gas will expand (increase) if the pressure on the gas sample is decreased and the volume of a sample of gas will contract (decrease) if the pressure on the gas sample is increased. [The pressure unit we will use with gases is atmosphere (atm) scale, which is mm/760]. Also, the pressure of a sample of gas will increase if the temperature of the gas sample is increased and the pressure of a sample of gas will decrease if the temperature of the gas sample is decreased. These facts can be expressed as a mathematical equation called the combined gas law which has the following form: This equation states that if the initial pressure (atm) of a gas is multiplied by its initial volume (liters) and is divided by its initial temperature (K) and a change is made in the pressure or the temperature causing a corresponding change in the volume, the final pressure (atm) multiplied by the final volume (liters) and divided by the final temperature (K) will still equal the same numerical value. This equation makes it possible to calculate one of these values if the other five are known. This equation should be used to do any gas problem in which two temperatures, volumes or pressures are given or asked for. If one of the quantities