 Chapter 5—Gases
 5.1: Substances That Exist as Gases
 Air: 78% N2, 21% O2, 1% Other (such as CO2)
 Ionic compounds do not exist as gases at 25 degrees Celsius as well as 1 atm (due to strong electrostatic forces holding cations/anions together in an ionic solid).
 The stronger the attractions (intermolecular forces), the less likely the compound can exist as a gas at ordinary temperatures.
 The characteristics of gases include: assuming the volume/shape of their containers, most compressible of the states of matter, will mix evenly/completely when confined in the same container, lower densities than liquids and solids.
 5.2: Pressure of A Gas
 Gas molecules are constantly in motion, causing them to exert pressure with the surfaces they come in contact with. Pressure is known as the most readily measurable properties of a gas.
 SI Units of Pressure
• Velocity is the change in distance with elapsed time. It uses the unit m/s or cm/s
• Velocity = distance moved/elapsed time
• Acceleration is the change in velocity with time. It uses the measurements of m/s2 or cm/s2
• Acceleration = change in velocity/elapsed time
• Second law of motion is formulated by Newton and this law defines force as mass times acceleration. The SI unit for force is newton (N): 1 N equals 1 kg m/s2
• Pressure is the force applied per unit area. The SI unit for pressure is pascal (Pa): 1 Pa equals 1 N/m2
• Pressure = force/area
 Atmospheric Pressure
• Air’s density decreases rapidly with the increasing distance form Earth. The force experienced by any area exposed to Earth’s atmospheric pressure is equal to the weight of the column of air above it.
• Atmospheric pressure is defined as the pressure exerted by Earth’s atmosphere. It depends on location, weather conditions and temperature.
• Air is like a fluid, the pressure it exerts on an object comes from all