# Gases - Kawameeh Middle School

Gases KMS 8th Grade Science Ms. Bormann The Nature of Gases The first gas to be studied was air & it was a long time before it was discovered that air was actually a mixture of particles rather than a single gas. Although air is a mixture of several different gases, it behaves much the same as any single gas. Regardless of their chemical identity, gases tend to exhibit similar physical behaviors

Characteristics of Gases The Kinetic Molecular Theory Kinetic = Motion Molecular = Molecules The theory states the tiny particles in all forms of matter are in constant motion. Boyles Law Robert Boyle was among the first to note the relationship between pressure and

of avolume gas. During his experiments temperature and theNOT amount of gas were allowed to change. Boyles Law states The pressure exerted by a gas held at constant temperature varies inversely with the volume of the gas.

For example: If the volume is halved, the pressure would be doubled Pressure Pressure amount of force exerted per unit of area. Pa = Pascal. SI unit for pressure. One Pascal of pressure is 1 Newton per square meter therefore a Pascal is a very small unit. kPa = kilopascal. A kilopascal is 1,000 Pa. Example: At sea level atmospheric pressure is 101.3 kPa. This means that at Earths surface, the atmosphere exerts a force of 101,300 Newtons on every square meter (this is about the weight of a large truck)

Atm = standard atmosphere. 101.3 kPa or 101,300 Pa Boyles Mathematical Law P1V1 = P2V2 A gas has a volume of 3.0 L at 2 atm. What is its volume at 4 atm? Boyles Law 1. Determine which variables you have

P1 = 2 atm V1 = 3.0 L P2 = 4 atm V2 = ? 2. Determine which law is being represented P P and

and V V= = Boyles Boyles Law Law 3. Rearrange the equation for the unknown variable. 4. Plug in the variables and solve. Charless Law

Jacques Charles was among the first to note the and volume relationship between temperatureof a gas. During his experiments pressure and NOT allowed toof change. the amount

gas are Charless Law states At constant pressure, the volume of a fixed number of particles of gas is directly proportional to the absolute (Kelvin) temperature For example: If the temperature is increased, the pressure will increase Temperature Charles' Law must be used with the Kelvin temperature scale.

This scale is an absolute temperature scale. At 0 K, there is no kinetic energy (Absolute Zero). According to Charles' Law, there would also be no volume at that temperature. This condition cannot be fulfilled because all known gases will liquefy or solidify before reaching 0 K. oC 273 Kelvin Charless Mathematical Law Eg: A gas has a volume of 3.0 L at

127C. What is its volume at 227 C? Charless Law 1. Determine which variables you have 2. TT11 = = 127C 127C + + 273 273 =

= 400K 400K V V11 = = 3.0 3.0 LL TT22 = = 227C 227C + + 273

273 = = 5ooK 5ooK which law is Determine V V22 = = ?? being represented. 3. Plug in variables

4. Cross multiply and solve

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