Due: Gay-Lussac’s Practice Problems Today – Overview of the Gas Laws and their Equations Ideal Gas Law HW – Ideal Gas Law WS Only Identify Variables and manipulate Equation for Practice Problems

Figure 5.1The three states of matter.

Gas LawVariables – Constant Variables – Change RelationshipEquation

The Gas Laws The gas laws describe the physical behavior of gases in terms of 4 variables: pressure (P) temperature (T) volume (V) amount (number of moles, n) An ideal gas is a gas that exhibits linear relationships among these variables. No ideal gas actually exists, but most simple gases behave nearly ideally at ordinary temperatures and pressures.

STP Revisited VariableValue Standard Pressure1 atm, 760 torr Standard Temperature273K Ambient 298K (room temp) Standard Molar VolumeMolar Volume Avagadro’s Hypothesis – 17 minAvagadro’s Hypothesis 22.4 L

Figure 5.9Standard molar volume.

Ideal Gas Law PV = nRT P = pressure in atm V = volume in liters n = moles R = proportionality constant = L atm/ mol·  T = temperature in Kelvins Holds closely at P < 1 atm

The Ideal Gas Law pV = nRT R = PV nT = 1 atm x L 1 mol x K = atm·L mol·K R is the universal gas constant; the numerical value of R depends on the units used.

Ideal Gases Ideal gases are imaginary gases that perfectly fit all of the assumptions of the kinetic molecular theory. Gases consist of tiny particles that are far apart relative to their size. Collisions between gas particles and between particles and the walls of the container are elastic collisions No kinetic energy is lost in elastic collisions

Ideal Gases Ideal Gases (continued) Gas particles are in constant, rapid motion. They therefore possess kinetic energy, the energy of motion There are no forces of attraction between gas particles The average kinetic energy of gas particles depends on temperature, not on the identity of the particle.

Ideal Gas Law Example Problem When filling a weather balloon with gas you have to consider that the gas will expand greatly as it rises and the pressure decreases. Let’s say you put about 10.0 moles of He gas into a balloon that can inflate to hold5000.0L. Currently, the balloon is not full because of the high pressure on the ground. What is the pressure when the balloon rises to a point where the temperature is -10.0°C and the balloon has completely filled with the gas.