The Caption Reads: Early morning fisherman on Lake Alexander near Motley, Minn, with a flock of birds as the states Walleye and Northern Pike season opened Saturday. Temperatures dipped below the freezing point, causing the 50 degree lake to steam as the sun began to rise.
AP Photo in a recent Newsday…
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Pressure =
Force
Area
F = mass X Acceleration
F = 10000 Kg X 9.8 m/sec2
F = 1 x 105 Kg m/sec2
F = 1 x 105 N(ewtons)
Pressure =
1 x 105 N
1 m2
=
1 x 105 N m2
=
1 x 105 Pa(scals)
=
100 k(ilo)Pa
SI Pressure Units Derivation
Pressure = Force per area
or the force of collisions per area
The translational movement of particles (atoms or molecules) creates the pressure when they collide. We will learn more about the factors that affect pressure but here temperature and pressure relationship is demonstrated.
Pressure drops due to combination of less gas particles and less kinetic energy as you generally increase in altitude.
Vapor Pressure - the force due to the collisions of gas molecules escaping from the gas phase.
The Force upward from the liquid molecules overcoming their attractive forces for each other creates VAPOR PRESSURE.
The molecules that have not evaporated do not have the kinetic energy to overcome the intermolecular attractions and remain as a liquid. Remember that Temperature is an average of all the different kinetic energies each molecules possess.
The Boltzmann distribution graph illustrates the molecules that reach the dividing line have enough energy to evaporate and contribute to a vapor pressure. As temperature increases more molecules have more energy to evaporate thus an increase in temperature is directly proportional to an increase in vapor pressure!
It really helps to visualise this upward force like this animation
https://www.youtube.com/watch?v=U1h6OFnBCUk
Another excellent way to visualise these physical changes. Notice some gas molecules are also condensing.
Because of condensation occurs at the same time as evaporation (equilibrium) we measure vapor pressure in a closed system.
Vapor Pressure For Water at Various Temperatures
Clearly as temperature increases the vapor pressure increases!!
Look at ice or water at 0 degrees celsius. There is some vapor pressure thus ice will sublime!
What is significant about the pressure at 100 degrees Celsius?
We can apply this table and the rate of evaporation of water and compare its intermolecular forces of attraction, vapor pressure, and boiling points with other liquids.
These four liquids and the results of this demo are illustrated in table H.
Standard Pressure
The same four liquids are illustrated here in Table H of your reference Table.
Notice the liquid that evaporated first has the steepest slope!
Temperature at which the liquids vapor pressure equals the atmospheric pressure = normal boiling point.
Notice that every liquid can boil at ANY temperature due the differences of the atmospheric pressure.
For instance if the atmospheric pressure is 120 kPa water will boil at 105 degrees Celsius.
Atmospheric Pressure
The Effects of Atmospheric Pressure on Boiling Points
The molecules of a liquid almost always have enough energy to overcome the intermolecular attractions that keep liquid molecules together but it is the atmospheric pressure that prevents the (maximum rate of evaporation) boiling. The lower the atmospheric pressure the lower the vapor pressure needed to match it and thus the boiling point is decreased. Raise the atmospheric pressure and more energy is needed to increase the vapor pressure enough to match the atmopheric pressure.
We can see this graphically:
Water boils at 105 degrees Celsius when the atmospheric pressure is 120 kPa
Water boils at 70 degrees Celsius when the atmospheric pressure is 30 kPa
The liquids are normal
The liquids are normal only at standard pressure thus their boiling points are almost never normal like sponge bob...
Effects of pressure on evaporation..
Alaska Pipeline Heat Exchangers-
Oil emerges from the ground at up to 180 °F (80 °C), and travels through the pipeline at temperatures above 120 °F (50 °C). In some elevated portions, heat conduction from the oil through the Vertical Support Members (VSMs) would melt the permafrost in which the VSMs are embedded. This would cause the pipeline to sink and possibly sustain damage. To prevent this from occurring, these portions of the pipeline include heat exchangers atop each VSM, passively cooled by convection to the air. Each heat exchanger is thermally coupled by a heat pipe to the base of the VTM. Running through the VSM, the heat pipe transports heat from the VTM base to the heat exchanger. Since ammonia, the heat pipe working fluid, has a boiling point lower than the permafrost, the heat pipe works throughout the year, even during the coldest winter nights. This relatively simple convection cooling system is thought by TAPS engineers and maintainers to be the greatest technological innovation associated with the pipeline.
Iodine Phase diagram – does it really sublime?
Intermolecular forces between iodine molecules are not strong enough to keep them together in a liquid state, after they gain enough kinetic energy to break free from the solid structure.
Application of Phase Diagrams
Diagram of a refrigerator
2. The hot NH3 (g) transfers its heat to the coils on the back of the refrigerator and the NH3 becomes a liquid.
NH3 (g) = NH3 (l) + Heat
.
NH3 (g) + Pressure = Hot NH3 (g)
3. The high pressure NH3 (l) flows through an expansion tube and pressure is lowered enough to cause vaporization which is endothermic cooling the system.
NH3 (l) + energy = NH3 (g)
1 .
2 .
3.
1
2
3
Caffeine dissolved from SCF