# CHEMISTRY Wednesday/Thursday April 25 th -26 th, 2012.

## Presentation on theme: "CHEMISTRY Wednesday/Thursday April 25 th -26 th, 2012."— Presentation transcript:

CHEMISTRY Wednesday/Thursday April 25 th -26 th, 2012

The Ideal Gas Law Moles of a gas –The number of moles of a gas will affect the pressure and volume – 1 mole of gas = 22.4 L or 22.4 dm 3 The relationship between pressure, volume, temperature, and number of moles is shown by the Ideal Gas Law: PV = nRT

The Ideal Gas Law PV = nRT This equation makes it possible to calculate any one of the properties- volume, pressure, temperature or moles of gas present- given the other three. –A gas that obeys this equation is said to behave ideally

The Ideal Gas Law In mathematical terms, this law is expressed as follows: PV = nRT P = pressure V = volume T = temperature (K) n = number of moles R = Universal gas constant (0.0821 L. atm/K. mol) Use Ideal Gas Law when P, V and T are NOT changing.

The Ideal Gas Law What pressure in atmospheres will 18.6 moles of methane exert when it is compressed in a 12.00-L tank at a temperature of 45°C? –As always, change the temperature to Kelvin before doing anything else. PV = nRT R = Universal gas constant (0.0821 L. atm/K. mol)

Pressure in a mixture of gases The total pressure of a mixture of gas is equal to the sum of the pressures each gas would exert by itself at the same volume This is Dalton’s Law –P Total = P 1 + P 2 + P 3 + … …

Standard Temperature and Pressure (STP) Conditions for STP: – 0 o C (273 K) – 1 atm (101.3 kPa)

Practice Problems If 300 mL of gas is collected at 4 atm, what volume will it occupy at 7 atm? A gas at 480 K occupies a volume of 200 mL. What volume will be occupied if the temperature drops to 273 K? At 360 K, a gas under 8 atm of pressure occupies 400 mL. What will the temperature be if the pressure drops to 6.5 atm and the volume is 582 mL? What is the pressure of a gas that originally occupied 6.79 dm 3 at a pressure of 80 kPa, if the volume is changed to 9.87 dm 3 A gas has a volume of 600 cm 3 at 49.5 deg C and exerts a pressure of 123.4 kPa. What pressure will it exert if it is moved at a 480 cm 3 container at 76 deg C?

Homework Ideal Gas Law w/s Gas Laws Quiz –Friday!!