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Studying Gases Good way to study the process of science. Distinguish between laws (what) and theories (why). Make observations. Use observations to develop theories. Make more observations. Continue.

Gases – Macroscopic Observations Gases take up the volume of the container. 1 cup of helium? Compressible Gases exert pressure. Basketballs, bike tires, etc. Explosions Density of a gas changes greatly with temperature. Gases mix well (diffusion). We can smell ammonia, vinegar, etc.

Clicker Question You are holding two balloons filled with air – a large balloon and a small balloon. What can be said about the relative pressure of air in each balloon? a) The pressure in the larger balloon is greater because there are more moles of gas. b) The pressure in the smaller balloon is greater because there is less space inside the balloon. c) The balloons have essentially the same pressure.

Take a Molecular Level View

Kinetic Molecular Theory Gases consist of particles in constant random motion. Pressure is due to collisions of gas particles with the container. Temperature is a measure of average kinetic energy.

V and n (KMT)

V and T (KMT) .

V vs. T(°C) (constant P, n)

V vs. T(K) (constant P, n)

P and T (KMT) .

P and V (KMT)

P vs. V (constant n, T)

PV/nT for Different Gases (all at 1 atm and 273K) O2: 0.082040 Latm/molK N2: 0.082059 Latm/molK CO2: 0.081538 Latm/molK NH3: 0.080875 Latm/molK Ar: 0.082040 Latm/molK