# 13.5 Phase changes

 Page 1 / 15
• Interpret a phase diagram.
• State Dalton’s law.
• Identify and describe the triple point of a gas from its phase diagram.
• Describe the state of equilibrium between a liquid and a gas, a liquid and a solid, and a gas and a solid.

Up to now, we have considered the behavior of ideal gases. Real gases are like ideal gases at high temperatures. At lower temperatures, however, the interactions between the molecules and their volumes cannot be ignored. The molecules are very close (condensation occurs) and there is a dramatic decrease in volume, as seen in [link] . The substance changes from a gas to a liquid. When a liquid is cooled to even lower temperatures, it becomes a solid. The volume never reaches zero because of the finite volume of the molecules.

High pressure may also cause a gas to change phase to a liquid. Carbon dioxide, for example, is a gas at room temperature and atmospheric pressure, but becomes a liquid under sufficiently high pressure. If the pressure is reduced, the temperature drops and the liquid carbon dioxide solidifies into a snow-like substance at the temperature $–\text{78}\text{º}\text{C}$ . Solid ${\text{CO}}_{2}$ is called “dry ice.” Another example of a gas that can be in a liquid phase is liquid nitrogen $\left({\text{LN}}_{2}\right)$ . ${\text{LN}}_{2}$ is made by liquefaction of atmospheric air (through compression and cooling). It boils at 77 K $\left(–\text{196}\text{º}\text{C}\right)$ at atmospheric pressure. ${\text{LN}}_{2}$ is useful as a refrigerant and allows for the preservation of blood, sperm, and other biological materials. It is also used to reduce noise in electronic sensors and equipment, and to help cool down their current-carrying wires. In dermatology, ${\text{LN}}_{2}$ is used to freeze and painlessly remove warts and other growths from the skin.

## PV Diagrams

We can examine aspects of the behavior of a substance by plotting a graph of pressure versus volume, called a PV diagram    . When the substance behaves like an ideal gas, the ideal gas law describes the relationship between its pressure and volume. That is,

$\phantom{\rule{0.25em}{0ex}}\text{PV}=\phantom{\rule{0.25em}{0ex}}\text{NkT}\phantom{\rule{0.25em}{0ex}}\left(\text{ideal gas}\right)\text{.}$

Now, assuming the number of molecules and the temperature are fixed,

$\text{PV}=\text{constant}\phantom{\rule{0.25em}{0ex}}\left(\text{ideal gas, constant temperature}\right)\text{.}$

For example, the volume of the gas will decrease as the pressure increases. If you plot the relationship $\text{PV}=\text{constant}$ on a $\text{PV}$ diagram, you find a hyperbola. [link] shows a graph of pressure versus volume. The hyperbolas represent ideal-gas behavior at various fixed temperatures, and are called isotherms . At lower temperatures, the curves begin to look less like hyperbolas—the gas is not behaving ideally and may even contain liquid. There is a critical point    —that is, a critical temperature    —above which liquid cannot exist. At sufficiently high pressure above the critical point, the gas will have the density of a liquid but will not condense. Carbon dioxide, for example, cannot be liquefied at a temperature above $\text{31}\text{.}0\text{º}\text{C}$ . Critical pressure is the minimum pressure needed for liquid to exist at the critical temperature. [link] lists representative critical temperatures and pressures.

what is mass
is the amount of an object
Sendawula
advantages of CRO over ordinary voltmeter
what is the difference between displacement and distance?!
what is equilibrium
If a system is said to be under equilibrium whenever there is no force act upon it... And it remain in its initial stage..
soniya
What is conductivity
It is the ease with which electrical charges or heat can be transmitted through a material or a solution.
Cffrrcvccgg
how to find magnitude and direction
how to caclculate for speed
Arjune
derivation of ohms law
derivation of resistance
Kazeem
R=v/I where R=resistor, v=voltage, I=current
Kazeem
magnitude
Arjune
A puck is moving on an air hockey table. Relative to an x, y coordinate system at time t 0 s, the x components of the puck’s ini￾tial velocity and acceleration are v0x 1.0 m/s and ax 2.0 m/s2 . The y components of the puck’s initial velocity and acceleration are v0y 2.0 m/s and ay 2.0
Arjune
Electric current is the flow of electrons
is there really flow of electrons exist?
babar
Yes It exists
Cffrrcvccgg
explain plz how electrons flow
babar
if electron flows from where first come and end the first one
babar
an electron will flow accross a conductor because or when it posseses kinectic energy
Cffrrcvccgg
electron can not flow jist trasmit electrical energy
ghulam
free electrons of conductor
ankita
electric means the flow heat current.
electric means the flow of heat current in a circuit.
Serah
What is electric
electric means?
ghulam
electric means the flow of heat current in a circuit.
Serah
electric means the flow of electric current through conductor
the continuos flow of electrons in a circuit is called electric
ANUBHA
electric means charge
ghulam
electric means current
flow of current.
Sendawula
a boy cycles continuously through a distance of 1.0km in 5minutes. calculate his average speed in ms-1(meter per second). how do I solve this
speed = distance/time be sure to convert the km to m and minutes to seconds check my utube video "mathwithmrv speed"
PhysicswithMrV
d=1.0km÷1000=0.001 t=5×60=300s s=d\t s=0.001/300=0.0000033m\s
Serah
A puck is moving on an air hockey table. Relative to an x, y coordinate system at time t 0 s, the x components of the puck’s ini￾tial velocity and acceleration are v0x 1.0 m/s and ax 2.0 m/s2 . The y components of the puck’s initial velocity and acceleration are v0y 2.0 m/s and ay 2.0
Arjune
D=1km=1000m t=5mins×60secs=300sec s=d/t=3.333m/s
Daniel
I think Daniel Glorious is ryt
Amalia
why we cannot use DC instead of AC in a transformer
becuse the d .c cannot travel for long distance trnsmission
ghulam
what is physics
branch of science which deals with matter energy and their relationship between them
ghulam
Life science
the
what is heat and temperature
how does sound affect temperature
sound is directly proportional to the temperature.
juny