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B. THERMAL PROPERTIES OF MATERIALS - Coggle Diagram
B. THERMAL PROPERTIES OF MATERIALS
Kinetic model of matter
o Matter consists of small particles.
o The particles are in constant motion.
o There are forces of attraction between the particles.
o Particles collide (with the sides of the container and each other) and exert pressure.
o Temperature of a substance is a measure of the average kinetic energy of the particles.
o A phase change may occur when the energy of particles changes.
Thermal expansion
Why there is an increase in volume with increase in temperature
o Heating a solid or liquid will increase the average kinetic energy of the particles.
o The forces holding the particles together do not change in strength, thus the particles now move in a bigger area.
o Thus, there is an overall increase in the volume called thermal expansion.
o The spaces between the particles increase, not the particles themselves.
A fractional change in the size of a material in response to a change in temperature
Examples
Train tracks have gaps
Long wires should not have too high a tension .
Bridges have rollers or expansion joints
Bimetallic strips are used in fire alarms and thermostats.
Linear thermal expansion
∆L = αL∆T
Volume thermal expansion
∆V = βV∆T
Anomalous behaviour of water and ice
Strong forces between particles
Hydrogen bonding is responsible for spaces in the lattice structure when it is a solid that hold air, making ice less dense than water
When liquid the average kinetic energy of particles is high enough to prevent forces to hold particles in fixed position
Specific heat capacity
The amount of heat required to change the temperature of 1 kg of material by 1 °C.
Q = mc∆T
The temperature change will be directly proportional to the amount of thermal energy supplied for a fixed mass of substance (ΔT ∝ Q).
The temperature is inversely proportional to the mass of substance for a fixed amount of thermal energy (ΔT ∝1 /m).
Phase changes
According to the kinetic model of matter
o A change of phase is the change of a substance from one physical form to another.
o All changes of phase are physical changes as the identity of the substance does not change
o After a change of phase particles will behave differently since the particles would have lost or gained energy during the change of state.
o NO CHANGE in the temperature as the average kinetic energy of the particles does not change during a phase change.
o During a phase change, the potential energy of the particles changes.
Boiling vs. evaporation
Boiling
Throughout the liquid
At the boiling point
The boiling point of a liquid is the temperature at which the vapor pressure of a liquid equals the external pressure surrounding the liquid
Evaporation
At the surface of the liquid
Below the boiling point of the liquid
Specific latent heat
The heat required for a phase change
Latent heat of vaporization (liquid to gas)
Q = mLv
The amount of heat required to change the phase of 1 kg of material without a change in temperature.
Latent heat of fusion (solid to liquid) Q = mLf
Various phase
changes
The changes of state indicated by the inside triangle in the diagram above require energy to be added to the substance and are endothermic processes.
The changes of state indicated by the outside triangle in the diagram above are processes where thermal energy is transferred to the surroundings and thus, are exothermic processes.