Lecture 1710/12/05

2 closed 1.0 L vessels contain 1 atm Br 2 (g) and 1 atm F 2 (g), respectively. When they are allowed to mix, they react to form BrF 5 (g). Assume that the temperature does not change. What is the pressure after the final reaction?

KINETIC MOLECULAR THEORY (KMT) Used to explain gas laws 1) A gas is composed of molecules whose size is much smaller than the distances between them. 1) i.e. most of the volume is empty space 2) So….gas can be easily compressed 3) So….gases can easily mix with one another

KINETIC MOLECULAR THEORY (KMT) 2. Gas molecules are in constant, rapid, random motion 1) Pressure of a gas is from the continual bombardment of the walls

KINETIC MOLECULAR THEORY (KMT) 3. Except when gas molecules collide, forces of attraction and repulsion between them are negligible.

KINETIC MOLECULAR THEORY (KMT) 4. When collisions between molecules occur, they are elastic 1. Total kinetic energy (KE) remains the same after collision 2. Molecules don’t run down

Kinetic Energy Equation for an individual particle m = massu = velocity Can’t use for collection of particles because of range of speeds

Velocity of Gas Molecules Molecules of a given gas have a range of speeds.

Average Kinetic Energy For a set of 1, 2, 3, 6: Compare the mean of the squares and the square of the mean

Root mean square (RMS) R= J/mol-K How does changing T or M change rms?

Velocity of Gas Molecules Lighter the molecules  faster the average speed