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Solids, liquids and gases occur due to the differences in the arrangement and freedom of movement of particles.
Diffusion movement of particles from an area of high concentration to an area of low concentration.
Diffusion experiments provide evidence for the existence of particles.
Boyle’s Law
At a constant temperature, the volume of a given mass of any gas is inversely proportional to the pressure of the gas
Pressure x Volume = Constant
Charles Law
At a constant temperature, the volume of a given mass of any gas is directly proportional to the Kelvin Temperature
Volume = Constant
Temperature
Gay-Lussac’s Law of Combining Volumes
When gases react, the volumes consumed in the reaction bear a simple whole number ratio to each other and the product when measured under same conditions of pressure and temperature
E.g. Ratio can be 1:1 but NOT 1.5:1
Combined Gas Law
P1 x V1 = P2 x V2
T1 T2
If a definite mass of gas occupies 250cm³ at a pressure of 100 000 Pa and a temperature of 91°C, what is the volume in cm³ at s.t.p.?
P1=100 000 Pa V1=250cm³ T1=91 + 273 = 364 Kelvin
P2=101 325 Pa V2= ??? T1=273 Kelvin <<< s.t.p.
100 000 x 250 = 101 325 x V2
364 273
V2 = 185cm³
Kinetic Theory of Gases
- Particle diameters are negligible compared to the distances between them
- No attractive or repulsive forces between particles
- Particles in constant rapid motion
- Average kinetic energy is proportional to Kelvin temperature
- All collisions are perfectly elastic
Ideal Gas obeys all assumptions of the kinetic theory under all conditions of pressure and temperature.
Equation of State for an Ideal Gas
PV=nRT
P = Pressure (Pa)
V = Volume (m³)
T = Temperature (K)
n = Number of Moles (mol)
R = Gas Constant (8.31 J/K/mol)
Mandatory Experiment: Determination of the Relative Molecular Mass (Mr) of a Volatile Liquid
Equipment: beaker, conical flask, aluminum foil, elastic band, mass scales,propanone, pin, clamp, water, thermometer, graduated cylinder, barometer
1. Two thirds fill a beaker and heat to almost boiling, keeping temperature constant.
2. Cover the mouth of a conical flask with aluminium foil and an elastic band. Find total mass of flask, foil and band.
3. Add 3 to 4 cm³ propanone to flask. Recover with foil, and use a pin to prick a small hole in the centre.
4. Attach clamp to flask and immerse in water, moving flask up and down.
5. When flask appears empty, remove flask immediately. Record exact temperature of water.
6. All flask to cool and thoroughly dry outside of flask. Find mass of flask, foil, band and contents and by subtraction, calculate mass of vaporised liquid.
7. Find volume of flask by filling it with water and transferring water to graduated cylinders.
8. Find room pressure using a barometer.
9. Calculate Relative Molecular Mass
Results
Mass of condensed vapour of volatile liquid: 0.67g
Atmospheric pressure: 100 812 Pa
Temperature of water: 368 K
Volume of flask: 0.00028 m³
n = PV/RT = 0.0092 moles
Mr = m/n = 0.67/0.0092 = 72.82
