SSS 1: KINETIC THEORY OF MATTER (I)
The Kinetic Theory of Matter states that all matter is made up of small particles that are in constant motion. The particles possess kinetic energy. The arrangement of these particles determine the physical state of the matter.
It also explains the behavior of matter based on the motion of its tiny particles (atoms or molecules).
Properties of the states of matter
The three states of matter are:
1. Solid state
2. Liquid State
3. Gaseous state
Solid State
1. They have definite shape and volume
2. They have strong intermolecular forces
3. Their particles are closely packed and orderly
4. Their particles are Incompressible
5. They have high density
6. Particles vibrate about fixed positions
Examples: Ice, iron, wood
Liquid State
1. They have no definite shape (they take the shape of their container)
2. They have definite volume
3. They have weaker intermolecular forces than solids
4. Their particles are close but can move past one another
5. They are slightly compressible
6. They have moderate density (less than solids but greater than gases/
Examples: Water, oil
Gaseous state
1. They have no definite shape (they take the shape of their container)
2. They have no definite volume (they expand to fill the container)
3. Their particles have very weak intermolecular forces
4. Their particles are far apart and move freely in all directions
5. They are highly compressible
6. They have a very low density
7. Particles move at high speed
8. Gases can flow easily (they are fluids)
9. They diffuse very rapidly
10. Exert pressure on the walls of their container
Examples: Air, oxygen, perfume vapour
Change of State
Change of state occurs as a result of a change in temperature (i.e. heating or cooling). When a substance is heated, its particles gain more kinetic energy and move faster, but when it is cooled, the particles lose kinetic energy and move more slowly.
Phenomena that support kinetic theory
The phenomena that support kinetic theory include:
1. Diffusion
2. Osmosis
3. Brownian motion
Diffusion
Diffusion is the movement of particles through a medium from a region of high concentration to a region of low concentration.
Example: Smell of perfume spreading in a room.
Diffusion of two gases
1. The white cloud formed is the ammonium chloride [NH₃Cl]
2. The cloud is formed close to the HCl because HCl(g) is a heavier gas and diffuses a shorter distance than ammonia [NH₃(g)] in the same amount of time.
Osmosis
osmosis is the spontaneous movement of a solvent, typically water, across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration.
Brownian Motion
Brownian motion is the random movement of tiny particles that are suspended in a fluid. They can be seen under a microscope.
Kinetic Theory of Gases
The kinetic theory of Gases states that:
1. Gas molecules move randomly in straight lines colliding with one another and with the wall of the container
2. The collisions of gas molecules are are perfectly elastic
3. The cohesive forces between the gas molecules are negligible
4. The temperature of the gases is a measure of the average kinetic energy of the gases
5. The actual volume occupied by the gas molecules themselves is negligible relative to the volume of the container
Temperature conversion
Temperature is a measure of the degree of hotness or coldness of a body. It shows how much heat energy is in a substance.
Temperature can be measured in three main units or scales:
1. Degree Celsius (°C)
2. Kelvin (K)
3. Fahrenheit (°F).
The normal human body temperature is 37°C (or 98.6°F).
The instrument used for measuring temperature is called a THERMOMETER.
BOYLE'S LAW
Boyle's Law states that the volume of a given mass of a gas is inversely proportional to its pressure provided that the temperature remains constant
Proportional Relationship:
V ∝ 1/P (V is inversely proportional to P)
V = k/P
P V = k
where: P = Pressure
V = Volume
k = a constant value for a given
sample of gas at a constant
temperature.
P₁V₁ = k and P₂V₂ = k, we can set them equal to each other. This gives us the most practical form of Boyle's Law:
P₁V₁ = P₂V₂
Where:
P₁ and V₁ are the initial pressure and
volume.
P₂ and V₂ are the final pressure and
volume
Note:
1. Standard temperature= 237K
2. Standard pressure = 760mmHg
= 1 atm
= 101,325 Nm⁻²
= 101,325 Pa
Simple calculations on Boyle's law
1. When the pressure on a gas increases at constant temperature, the volume will (a) increase (b) decrease (c) remain constant (d) first increase then decrease
2. The volume of a given mass of a gas at 10°C and 600mmHg is 140cm³. What will be the volume of the gas at 10°C, if the pressure is 1200mmHg.
Solution:
P₁V₁ = P₂V₂
600 x 140 = 1200 x V₂
84000 = 1200 x V₂
V₂ = 84000 / 1200
V₂ = 70cm³
3. A sample of oxygen gas has a volume of 220 mL when its pressure is 2.2 atm. What will the volume of the gas be at a pressure of 1.2 atm if the temperature remains constant?
Solution:
Initial Volume (V₁) = 220 mL
Initial Pressure (P₁) = 2.2 atm
Final Pressure (P₂) = 1.2 atm
To Find: Final Volume (V₂) = ?
We can calculate the final volume of the gas using Boyle’s law.
P₁V₁ = P₂V₂
2.2 × 220 = 1.2 × V₂
484 = 1.2 × V₂
484 / 1.2 = V₂
V₂ = 403.33 mL ≈ 403mL
Class activities
A certain volume of a gas at 20°C has a pressure of 400mmHg. If at the same temperature, this pressure is decreased to 200mmHg, the gas has now occupying a volume of 100cm³. Calculate the initial volume of the gas.
Charles Law
The volume of a given mass of gas is directly proportional to its absolute temperature provided the pressure remains constant.
V ∝ T
When volume (V) is plotted against temperature (T in Kelvin), the graph is a straight line passing through the origin.
If temperature is measured in °C, the line cuts the temperature axis at –273°C, known as absolute zero.
Absolute Zero
Absolute zero (–273°C or 0 K) is the lowest possible temperature where the volume of a gas theoretically becomes zero and molecular motion stops.
Example:
T₁ = 27 + 273 = 300K
T₂ = 127 + 273 = 400K
V₂ = ?
200/300 = V₂/400
V₂ = (200 × 400)/300
V₂ = 266.7cm³
General gas equation
Gases have properties such as Pressure (P), Volume (V) and Temperature (T) that are interrelated. The relationship between these three variables is summarized by the Gas Laws
1. Boyles Law: relationship between pressure and volume at constant temperature
2. Charles Law: relationship between volume and temperature at constant pressure
3. Pressure Law: relationship between pressure and temperature at constant volume
These three can be combined to form one single expression known as the General Gas Equation
T₁ = 27 + 273 = 300K
P₁ = 100Kpa = 100,000pa
V₂ = ?
T₂ = 47 + 273 = 320K
P₂ = 120Kpa = 120,000pa
V₂ = (P₁V₁T₂)/(P₂T₁)
V₂ = (100000×200×320)/(120000×300)
V₂ = 178cm³
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