- Organic Chemistry
- Aldehydes and Ketones
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- Amines and other nitrogen compounds
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- Chemistry in daily life
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- Nomenclature and isomerism

# 218 - Physical Chemistry Questions Answers

**Select Topic:**Solid State

### TIPS FOR SOLID STATE

The Seven Crystal Systems

Triclinic The triclinic unit cell is defined by three axes, a, b, and c, of unequal lengths.

None of the angles, alpha, beta, and gamma, between these axes are exactly 90°.

The standard convention for assigning axes is c < a < b.

The angle alpha lies between the b and c axes; beta lies between a and c,

and gamma lies between a and b. The cell is usually chosen

so that alpha and beta are obtuse (between 90º and 180º).

Orthorhombic

The orthorhombic unit cell is defined by three axes, a, b, and c, of unequal lengths.

The angles between all axes are exactly 90°.

The axes are chosen to correspond to 2-fold axes of rotational symmetry axis

or to be perpendicular to mirror symmetry planes. The standard convention is that

c < a < b.

Hexagonal

The hexagonal unit cell can be defined by three axes. Two of them, labeled a are equal

in length and at an angle of 120º to one another. The third axis, labeled c, is

perpendicular to the a axes and of a different length.

The c axis corresponds to a 3-fold or 6-fold symmetry axis.

To highlight the presence of 3-fold or 6-fold symmetry,

usual practice is to include a third a axis at 120° to the other two,

and correspondingly to use a redundant 4th integer in the Miller index.

(The extra integer is placed in the 3rd position and equals the negative of the

sum of the first two).

Trigonal

A subgroup of the hexagonal crystal system characterized by one three-fold symmetry axis.

The remaining crystal systems in the hexagonal crystal system have a six-fold symmetry axis

Monoclinic

The monoclinic unit cell is defined by three axes, a, b, and c, of unequal lengths.

The angles between the a and b axes and between the c and b axes are exactly 90°.

The b axis is chosen to correspond to a 2-fold axis of rotational symmetry axis

or to be perpendicular to a mirror symmetry plane.

The standard convention for assigning the other axes is c < a.

The unit cell is also chosen so that the angle beta, lying between the a and c axes

is obtuse (between 90º and 180º).

Tetragonal

The tetragonal unit cell is defined by three axes. Two of them, labeled a, are equal

in length; and the c axis is of a different length. All angles between axes are 90°.

The c axis corresponds to a symmetry axis of either 4-fold rotation or

4-fold rotation inversion. The c axis can be either longer or shorter than the a axes.

Isometric, Cubic

The isometric (=cubic) unit cell is defined by three axes of equal length, all labeled a.

All angles between axes are 90°. Because of the equivalence of all axes and angles.

The isometric system can contain combinations of many different types of symmetry elements:

2-, 3-, and 4- fold rotation axes, 3- and 4- fold rotation-inversion axes,

mirror planes, and centers of symmetry

**Submit By: MANISH SIR**6 year ago

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20 ml of 0.5M hcl is mixed with 30ml of 0.3Mhcl . xmolarity ?

**Asked By: SIDDHARTHINI**7 Month ago

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**submit your answer**for the melting point of NaCl heat required is 7.26 kcal/mole and entropy increases by 6.73 cal/mol/k.the melting point of the salt

**Asked By: SANGEETHA**1 year ago

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**submit your answer**If Ka is 10 then find its pH VALUE?

**Asked By: DR SUNITHA NAIDU**1 year ago

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**submit your answer**
entropy of vaporisation of water at 100°C if molar heat of vaporisation is9710 cal/ mo

**Asked By: ANAMIKA MEENA**2 year ago

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**submit your answer**the enthalpies of neutralisation of a weak acid HA and a weak acid HB by NaOH are -6900 cal/equivalent and -2900 cal/equivalent, respectively. when one equivalent of NaOH is added to a solution containing one equivalent of HA and one equivalent of HB the enthalpy change was -3900 cal. in what ratio is the ratio is the base distributed between HB and HA?

**Asked By: AISHA SIDDIQUI**2 year ago

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**submit your answer**- In a solid ‘AB’, ‘A’ atoms have ccp arrangement and B atoms occupy all the octahedral voids. If all the face centred atoms along one of the axes are removed, then what will be the formula of the compound?

**Asked By: BEN TENISON**2 year ago

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**submit your answer**### If value of n+l is more than 3 and less than 6 then what will be possible number of orbitals?[Atomic structure]

**Asked By: TARKESHWAR KUMAR**2 year ago

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