Gases - Leaving Cert HL Chemistry

what is a gas?

a gas is a state of matter. particles in a gas have large spaces between them. particles in gas move quickly and randomly.

kelvin conversion

C + 273

standard temperature

273K

standard pressure

100kPa

Boyle’s Law

the volume of a fixed mass of gas is inversley proportional to its pressure, at constant temperature.

Charles’ Law

the volume of a fixed mass of a gas is directly proportional to its temperature, at constant pressure.

Combined Gas Law Equation

P1V1/T1 = P2V2/T2

Gay-Lussac’s Law of Combining Volumes

in a reaction between gases, the volumes of the reacting gases and the volumes of any gaseous products are in the ratio of small whole numbers, at constant pressure and temperature

Avogadro’s Law

equal volumes of different gases at the same temperature and pressure contain the same number of molecules

Ideal Gas Equation

PV=nRT

ideal gas equation units

temp - K

pressure - Pa

volume - m3

gas constant - 8.31

Five Assumptions of the Kinetic Thoery of Gases

1. gases are made up of particles that are in continuous motion

2. gaseous molecules are independent of each other - no attractive or repulsive forces

3. the volume of gaseous molecules is negligible compared to the space occupied

4. when molecules collide, there is no loss of energy - collisions are perfectly elastic

5. the kinetic energy of the molecules is proporional to the temperature in K

Ideal Gas

a gas that obeys all the assumptions of kinetic theory under all conditions of temperature and pressure.

two limitations of the kinetic theory of gases

1. polar gaseous molecules (NH3, HCl) have attractive forces between them

2. under high pressure and low temperatuure, the volume of the molecules is not negligible

Measure the relative molecular mass of a volatile liquid

1. find mass of conical flask, foil, and rubber band

2. approx. 10cm3 volatile liquid (propanone or cyclohexane) poured into flask

3. foil placed over mouth of flask, held in place with rubber band

4. pinhole made in foil

5. flask damped in beaker of boiling water util the volatile liquid has vapourised

6. temperature of water measured with thermometer

7. atmospheric pressure measured using barometer

8. flask removed and allowed to cool to room temperature

9. outside of flask and foil are dried

10. flask, foil, and rubber band are reweighed

11. volume of conical flask is found by filling it completely with water, and in portions, pouring it out into a graduated cylinder