NDIAN SCHOOL AL WADI AL KABIR
DEPARTMENT OF SCIENCE 2016 – 2017
SUMMARY NOTES – STATES OF MATTER
van der Waals forces : Attractive interactions between two particles are called van der Waals forces.
They are of the following types.
Dispersion forces or London forces
- Exists in atoms and non polar molecules
- The atoms are electrically symmetrical because their electronic charge is symmetrically distributed.
- But a dipole may be induced momentarily in one of the atoms.
-This instantaneous dipole may induce dipole in the neighbouring atom.
-The force of attraction between these temporary dipoles is called London forces.
-Interaction Energy α 1/r6where r is the distance between the two particles.
Dipole – Dipole forces
- Exists in polar molecules having permanent dipoles.
-They will have partial charges.
- H bond is an example of dipole dipole forces.
- Interaction Energy α 1/r6 (rotating polar molecules)
α 1/r3 (stationary polar molecules)
Dipole – Induced dipole forces
- Exists between a polar and a non polar molecule.
- The permanent dipole of the polar molecule induces dipole in the non polar molecule and thus makes the latter
polar.
- Interaction Energy α 1/r6
- These forces depend on the polarizing power of one and the polarizability of the other.
1. What happens to intermolecular forces with temperature?
With rise in temperature, the molecules move apart and the intermolecular forces become lesser.
Solids → Liquids → Gases
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2. What are the characteristics of gaseous state?
- Gases are highly compressible.
- Gases exert pressure in all directions.
- Gases have much lower density than solids and liquids.
- They assume the volume of the container.
- Gases mix completely in all proportions.
3. What are Gas laws?
Gas laws are those which give the various properties and characteristics of gases
Boyle’s law
The law states that the pressure of a fixed amount of gas is inversely proportional to its volume at constant
pressure.
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p α𝑉 (at constant T and n)
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p = k1𝑉 ( k1 is the proportionality constant)
pV = k1
If a fixed amount of gas undergoes expansion from V1to V2 at p1 and p2 respectively, then
p1V1 = p2V2 = constant
Isotherm
Each curve obtained on a p vs Volume graph at constant temperature is called an isotherm.
p vs Volume graph
p vs 1/V graph
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Charles’ law
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It was found that for every 1º rise in temperature, the volume of a gas increases by 273.15of the original volume.
Let V0and Vt be the volumes at 0 ºC and t ºC respectively then
𝑡
Vt = V0 + 273.15 V0
= V0 (1 +
𝑡
273.15
273.15+𝑡
= V0 (
273.15
)
)
At this stage ,a new scale of temperature was defined called Kelvin temperature scale or thermodynamic scale
or absolute temperature scale.
Here 273.15 + t = Ttand 273.15 = T0
In general it can be written as
i.e V/T = constant = k2
V = k2 T
V α T (n and p)
Thus Charles’ law states that the volume of a fixed mass of gas is directly proportional to the absolute
temperature at constant pressure.
Isobar
Each line on Volume vs temperature graph at constant pressure is called isobar.
Absolute temperature
The lowest hypothetical or imaginary temperature at which gases are supposed to occupy zero volume is called
Absolute zero.
Prepared by Ms. Jasmin J
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