Gases

Kinetic Molecular Theory The kinetic molecular theory is used to explain the behavior of gases. All matter is made up of particles called atoms. The atoms are in constant motion. Collisions between the particles are elastic (no energy is gained or lost due to the collision).

Properties used to describe gases. The following four properties are used to describe gases: Temperature (oC or K)-how fast the particles making up the gas are moving. Volume (L)-the amount of space the gas occupies (usually the size of the container) Amount of sample (moles)-# of particles in the sample Pressure (atm, kPa, mm Hg, torrs)

Pressure Pressure is the force that is exerted on a surface. P = F/A Units for pressure are N/m2 One pascal (Pa) = 1 N/m2

Gases and Pressure Gases exert pressure due to the collisions between the molecules and the walls of the container. The atmosphere exerts a pressure of 14.7 lbs/in2. Gravity acts as the atmosphere’s container.

The atmosphere exerts a pressure that can support a column of mercury 760 mm tall. 1 atm of pressure = 760 mm Hg = 14.7 lbs/in2 = 101.3 kPa

Measuring Pressure The device used to measure pressure is a manometer. A barometer is a specific type of manometer used to measure air pressure. Open Manometer Closed Manometer

Manometer Problems

The Components of the Atmosphere The atmosphere consists of the following gases: Nitrogen (N2) = 78% Oxygen (O2) = 21 % Argon (Ar) = 0.93% Carbon Dioxide (CO2) = 0.038%

Gas Laws

Boyle’s Law At constant temperature, the pressure and volume of a gas are inversely related. (The number of gas particles remains constant). As pressure increases, volume decreases. Examples/Applications of Boyle’s Law: Opening a soft drink bottle Ears popping when an airplane takes off A bicycle pump Scuba diving

Charles’ Law At constant pressure, the Kelvin temperature and volume of a gas are directly related. (The number of gas particles remains constant). As temperature increases, volume increases. Examples/Applications of Charles’ Law: Bread rising in the oven Car tires appearing to be flat in the morning A balloon pops if left in a hot car

Gay-Lussac’s Law At constant volume, the Kelvin temperature and pressure of a gas are directly related. (The number of gas particles remains constant). As temperature increases, pressure increases. Everyday Examples/Applications of Gay-Lussac’s Law: An aerosol can explodes if left in a fire. A pressure cooker http://preparatorychemistry.com/Bishop_Gay_Lussac_frames.htm