States of Matter and Thermal Expansion

States of Matter

• The lecture will cover states of matter
• Key topics will be temperature change mechanisms, the 5 phases of matter, differentiating between phases and latent heat

Phases of Matter

• The three most commonly known states of matter are solids, liquids, and gases
• Adding energy changes the phase of a substance
• Alternatively subtracting heat will change the phase of a substance

Solids

• At the atomic and molecular scale, solids are highly ordered and have organised structures with crystal properties
• Even powders are made of millions of micro-crystals
• The atoms in a solid occupy lattice points arranged periodically in every direction in a crystal
• Atoms in the crystal lattice vibrate about their equilibrium lattice positions
• As temperature increases, the amplitude and frequency of vibration also increases, leading to thermal expansion
• If the temperature continues to rise, the vibrations become so strong that the lattice breaks apart, known as melting
• Solids melt and become liquid

Liquids

• Particles in a liquid are further apart than in a solid, but are still able to attract each other
• Liquids are not arranged in a regular pattern and have no inherent shape
• Liquids can be moulded into any form by placing it in a container
• Liquid molecules are not rigidly bound, allowing fast movement
• Some molecules have enough kinetic energy to escape from the bulk liquid; process called evaporation
• Rate of evaporation increases with temperature
• Molecules evaporating from a liquid surface generate Vapor Pressure (VP)
• At Equilibrium, the number of molecules evaporating equals the number of vapor molecules re-entering the liquid
• Vapor Pressure increases as temperature increases
• The temperature at which the VP equals atmospheric pressure (Patm) is known as the Boiling Point (BP)
• At the Boiling Point, visible evaporation occurs throughout the bulk of the liquid
• The Boiling Point is the only temperature at which a liquid and its vapor can coexist in equilibrium for a given pressure

Gases

• Heating a liquid gives particles more energy, causing them to move faster
• The atoms can escape from the liquids surface becoming a gas
• The particles in gas move around very fast and cannot attract each other

Latent Heats

• Latent heat of fusion is 6kJ/mol (3.3 x 10^5 J/kg) - energy to change from solid to liquid at the same temperature
• Latent heat of vaporisation is 41kJ/mol (22.6 x 10^5 J/kg)- the energy to change from a liquid to a gas at the same temperature
• The energy required to convert 1kg of solid to 1kg of liquid at the same temperature is the Specific Latent Heat of Fusion (Lf)
• The energy required to convert 1kg of liquid to 1kg of gas at the same temperature is the Specific Latent Heat of Vaporisation (Lv)
• In almost all cases, Lf is much less than Lv
• Some mammals use Lv to cool themselves by evaporating liquids on the skin surface
• In snowy conditions, birds require more twice as much heat to melt snow than heat their body

Phase Diagrams

• Temperature at which phase change occurs varies with the absolute pressure
• The Triple Point on the phase diagram signifies the only conditions under which all three phases (solid, liquid, and gas) can exist simultaneously
• It is possible to boil water at a temp less than 100°C if the gas pressure above the liquid surface is lowered

Phase Diagram CO2

• The triple point of CO2 is at temp = -56.6°C and pressure = 5.1 atm
• Liquid CO2 can never exist at standard atmospheric pressure
• Reducing the pressure sufficiently can cause to skip the liquid phase completely and go straight from solid to gas phase, called Sublimation
• Freeze-drying is also possible by the same principle

Other States of Matter

• There are two other Phases/States of matter and they occupy opposite ends of the energy/heat spectrum
• Removing almost all the heat energy from a small group of inert atoms leads to the Quantum Mechanical state
• Bose-Einstein Condensate occurs at micro-Kelvin Temperatures, where atoms occupy identical ground states
• Plasma requires so much energy that all electrons are ionized off the atom resulting the final state of matter
• A plasma is a rarified gaseous soup of positive and negative ions, highly reactive, which is used settings for disinfection
• Aurora Borealis/Australis is an example of plasma activity

Learn about the fundamental states of matter: solids, liquids, and gases, and how energy changes affect these phases. Explore the atomic structure of solids, including crystal properties and lattice arrangements. Understand thermal expansion and the effect of temperature on atomic vibrations within solids.