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How do macroscopic observations provide a model of the microscopic properties of a substance?
How do macroscopic observations provide a model of the microscopic properties of a substance?
Macroscopic observations like temperature, pressure, volume, and phase (solid, liquid, gas) help build a molecular model of matter:
In solids, macroscopic rigidity suggests particles are tightly packed and vibrate about fixed positions.
In liquids, the ability to flow but maintain volume shows that particles are close together but can move past each other.
In gases, compressibility and expansion suggest particles are far apart and moving freely at high speeds.
Temperature readings (Kelvin or Celsius) correlate with the average kinetic energy of particles: Kelvin temperature∝average kinetic energy of molecules
Density measurements () reveal how closely packed the particles are in different states of matter.
Phase changes (e.g., melting, boiling) observed at constant temperature imply changes in intermolecular potential energy, not kinetic energy.
How can observations of one physical quantity be used to determine the other properties of a system?
How can observations of one physical quantity be used to determine the other properties of a system?
Measuring temperature change ΔT and knowing the specific heat capacity ccc allows you to find the thermal energy transfer Q.
Observing a phase change at constant temperature, and measuring the energy absorbed or released, gives information about the latent heat
Observing the direction of heat flow tells us which object has the higher temperature (since heat flows from higher to lower temperature).
The rate of energy transfer can indicate properties like thermal conductivity if studied carefully.
Understandings
Understandings
molecular theory in solids, liquids and gases
density
that Kelvin and Celsius scales are used to express temperature
that the change in temperature of a system is the same when expressed with the Kelvin or Celsius scales
that Kelvin temperature is a measure of the average kinetic energy of particles
that the internal energy of a system is the total intermolecular potential energy arising from the forces between the molecules plus the total random kinetic energy of the molecules arising from their random motion
that temperature difference determines the direction of the resultant thermal energy transfer between bodies
that a phase change represents a change in particle behaviour arising from a change in energy at constant temperature
quantitative analysis of thermal energy transfers Q with the use of specific heat capacity c and specific latent heat of fusion and vaporisation of substances L
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