Density and Pressure
Density and Pressure
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Define density
Understand relative density
Define and use the term pressure
Learn the instruments used for measuring
pressure
• Brownian Motion and the Kinetic Model
• Pressure in a Gas
• Melting, Boiling and Evaporation
Density
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Mass per unit volume
Units: kgm-3, gcm-3, gml-1
Density is changes with temperature
Relative Density
– Density of a substance divided density of water
– Dimensionless
– Density of water is 1000 kgm-3
Densities of Some Substances
Comparing Densities
• When most substances change from a solid
state to a liquid state their volume does not
change much.
– Density of a solid is almost the same as a liquid.
Comparing Densities
• When a liquid changes into a gas, the spacing
between the particles increases by a factor of
about ten.
• As a result, the density of a substance
decreases by a factor of approximately 1000
when it changes from a liquid to a gas.
Sample Calculations
• A cup of gold colored metal beads was measured to
have a mass 425 grams. By water displacement, the
volume of the beads was calculated to be 48.0
cm3. Identify the metal.
• A 60-ml flask is filled with mercury at 0C. When the
temperature rises to 80C, 1.47 g of mercury spills
out of the flask. Assuming that the volume of the
flask is constant, find the density of mercury at 80C
if its density at 0C is 13,645 kgm-3.
Pressure
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Force per unit area
Force is normal to the area
Units: Nm-2, kgm-1s-2, Pascal (Pa)
Fluid Pressure
Equation
Fluid Pressure
• Equation
• Absolute pressure
• Gauge pressure
Measuring Pressure
• Mercury Barometer
• U-tube Manometer
• Equation
Sample Calculations
• A U-tube contains liquid of unknown density.
An oil of density 800 kgm-3 is poured into one
arm of the tube until the oil column is 12 cm
high. The oil-air interface is 5.0 cm above the
liquid level in the other arm of the tube. Find
the density of the liquid.
• P400, #22.18 (a)
Brownian Motion
Brownian Motion
Brownian Motion Video 1
Brownian Motion Video 2
Kinetic Theory of Matter
All matter is made up of
a large number of tiny atoms or molecules
which are in continuous motion
Pressure of a Gas
• Force that the gas molecules exert as they hit
the walls of the container
Energies and Molecules
• Potential Energy
• Distance between molecules
• Kinetic Energy
• Related to temperature of the substance
• Internal Energy
• The sum of the kinetic and potential energies of a
substance.
Melting and Boiling
• Heat is added to break bonds between
molecules
• Some part of the energy is used to work
against the environment
• Both occur at a specific constant temperature
• Let us look at the energies involved
Boiling and Evaporation
• Both involve changes from liquid to gas
• Boiling occurs at a specific temperature
• Evaporation occurs at any temperature
• Boiling occurs inside the liquid
• Evaporation occurs at the surface of the liquid