= Let’s Build It…

= If the temperature of the gases in the soda increase, what happens to the pressure inside the can?

= So Pressure and Temperature are __________ related

= So Pressure and Temperature are directly related

= They must go on opposite sides of the equation. “If one increases, the other must increase”.

= If the temperature of the gas in the balloon decreases, what happens to the volume of the balloon?

= So Volume and Temperature are __________ related

= So Volume and Temperature are directly related

= They must go on opposite sides of the equation. “If one decreases, the other must decrease”.

= If you add moles of gas to the tire, what happens to the volume and the pressure in the tire?

= So Volume and Pressure are __________ related to Moles

= So Volume and Pressure are directly related to Moles

= They must go on opposite sides of the equation. “If one increases, the other must increase”.

= There is also a “constant” of proportionality in the equation

= It is called “R”, the “Universal Gas Law Constant”

= This law is valid under most normal conditions so don’t break it!

= Volume is measured in Liters (L)

= Amount is measured in Moles (mol)

= Temperature is measured in Kelvins (K)

= Pressure has many units. The S.I. unit for pressure is the Pascal (Pa) *See the notes on “Pressure” to learn more

= “R” has 4 units. Rearrange this equation to solve it for “R”

= See why it has 4 units, now?

= “R” has units of pressure

= “R” has units of pressure, volume

= “R” has units of pressure, volume, moles

= “R” has units of pressure, volume, moles and temperature

= To get the numerical value of “R”, you must substitute in all the standard values: (1 atm)(22.4L) (1mol)(273K) atm L mol K

= There are many different standard pressure units you could plug in: (760mmHg)(22.4L) (1mol)(273K) mmHg L mol K 62.4

= There are many different standard pressure units you could plug in: (101.3kPa)(22.4L) (1mol)(273K) kPa L mol K 8.31

What is the volume of 2.3 moles of hydrogen gas at a pressure of 1.2 atm and a temperature of 20 o C? If PV=nRT, then V = nRT P

What is the volume of 2.3 moles of hydrogen gas at a pressure of 1.2 atm and a temperature of 20 o C? V = (2.3 mol) atm L mol K (293 K) (1.2 atm)

V = (2.3 mol) atm L mol K (293 K) (1.2 atm) This “R” value has atm in it

V = (2.3 mol) atm L mol K (293 K) (1.2 atm) This “R” value has atm in it which cancels with units of “P”

V = (2.3 mol) atm L mol K (293 K) (1.2 atm) Every unit cancels except “L” which is good because we are solving for volume!

What is the volume of 2.3 moles of hydrogen gas at a pressure of 1.2 atm and a temperature of 20 o C? V =46 L

What is the temperature of 2.50 moles of helium gas at a pressure of 795 mmHg in a 3.25 liter container? If PV=nRT, then T = PV nR

What is the temperature of 2.50 moles of helium gas at a pressure of 795 mmHg in a 3.25 liter container? If you want to use atm L for “R”, mol K you have to convert 795 mmHg to atm so they will cancel

What is the temperature of 2.50 moles of helium gas at a pressure of 795 mmHg in a 3.25 liter container? 795 mmHg x 1 atm = 760 mmHg 1.05 atm

What is the temperature of 2.50 moles of helium gas at a pressure of 795 mmHg in a 3.25 liter container? T = (2.50 mol) atm L mol K (3.25 L)(1.05 atm)

T = (2.50 mol) atm L mol K (3.25 L)(1.05 atm) Every unit cancels except “K” which is good because we are solving for temperature!

What is the temperature of 2.50 moles of helium gas at a pressure of 795 mmHg in a 3.25 liter container? T =16.6 K

A gas that behaves according to the Kinetic Molecular Theory* (It obeys all the postulates of KMT) *See KMT Notes for more information

Never!!!! Ideal gases don’t exist However, real gases act like “ideal” gases at most normal conditions of temperature and pressure

Real gases follow the Kinetic Molecular Theory until……. The temperature gets extremely low OR The pressure gets extremely high

The KMT says particles don’t attract or repel each other, but at very low temperatures, gas particles move very slowly and this allows particles to attract each other when they get close If no attractive forces, the particles will spread out If attractive forces are present, The particles would clump together

The KMT says particles don’t attract or repel each other, but at very low temperatures, gas particles move very slowly and this allows particles to attract each other when they get close If no attractive forces, the particles will spread out And the volume would be smaller Than our gas law would predict

The KMT says particles have negligible volume, but at very high pressures, the gas particles are smashed close together thus reducing the empty space between them, but NOT to zero volume because the particles themselves have some volume.

Because it is a useful “model” that helps us understand and predict what gases will do under most conditions The KMT only breaks down under extremely low temperatures and extremely high pressures