Diamond is hard because from Chemistry JEE Year 2008 Free Solved

Subject

Chemistry

Class

JEE Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

The number of hydrogen atoms present in 25.6 g of sucrose (C12H22O11) which has a molar mass of 342.3 g is

  • 22 × 1023

  • 9.91 × 1023

  • 11 × 1023

  • 44 × 1023 H atoms


2.

The oxidation number of oxygen in KO3, Na2O2 is

  • 3, 2

  • 1, 0

  • 0, 1

  • -0.33, -1


3.

The number of formula units of calcium fluoride, CaF2 present in 146.4 g of CaF(the molar mass of CaF2is 78.08 g/mol) is

  • 1.129 × 1024 CaF2

  • 1.146 × 1024 CaF2

  • 7.808 × 1024 CaF2

  • 1.877 × 1024 CaF2


4.

The standard free energy change of a reaction is G°= -115 kJ at 298 K. Calculate the equilibrium constant Kp in log Kp (R =8.314 JK -1mol-1 ).

  • 20.16

  • 2.303

  • 2.016

  • 13.83


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5.

If an endothermic reaction occurs spontaneously at constant temperature (T) and pressure (p), then which of the following is true?

  • G > 0

  • H < 0

  • S > 0

  • S < 0


6.

A spontaneous process is one in which the system suffer

  • no energy change

  • a lowering of free energy

  • a lowering of entropy

  • an increase in internal energy


7.

CH3CH3 + HNO3 675K ?

  • CH3CH2NO2

  • CH3CH2NO2 + CH3NO2

  • 2CH3NO2

  • CH2= CH2


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8.

Diamond is hard because

  • all the four valence electrons are bonded to each carbon atoms by covalent bonds

  • it is a giant molecule

  • it is made up of carbon atoms

  • it cannot be burnt


A.

all the four valence electrons are bonded to each carbon atoms by covalent bonds

In diamond each carbon atom is linked to four other carbon atoms by sigma bond. Each σC - C bond is formed by the overlapping of sp3 hybrid orbitals of each carbon atoms. Each carbon atom is present at the centre of a regular tetrahedron. Each carbon atom is surrounded by four other carbon atoms present at the corners of a regular tetrahedron. The octet of each carbon atom is complete. Structure of diamond is a rigid three dimensional network. This explain high density and hardness of diamond. Diamond is chemically inactive due to rigid three dimensional structure.
High energy is required to break the large number of σC - C bonds present in diamond. This explain the high melting point of diamond.

                                           


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9.

The gas evolved on heating alkali formate with soda-lime is

  • CO

  • CO2

  • hydrogen

  • water vapour


10.

The continuous phase contains the dispersed phase throughout, example is

  • water in milk

  • fat in milk

  • water droplets in mist

  • oil in water


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