Explain the formation of H2 molecule on the basis of valence bond theory.
When hydrogen atoms combine to form molecules of hydrogen, 433 KJ/mol. energy is released.
Whenever atoms combine to form a molecule, there is always decrease in the energy. Actually, when two H atoms are far separated, they do not have any force of interaction (attractive or repulsive). As they tend to come closer, two different forces operates:
(a) The nucleus of one H is attracted towards the electrons of the other H atoms and Vice-versa. The energy is released in attraction.
(b) The nuclei of the atoms as well as their electrons repel each other. Energy is needed to overcome the force of repulsion.
Now in case, if the magnitude of the attractive forces is more than that of the repulsive forces, a stable molecule will be formed.
However, if the repulsive forces are more than the attractive forces, then the atoms will not combine.
If for example HA & HB are two hydrogen atoms & eA & eB are their respective electrons, then attractive & repulsive forces may be shown as follows:
------------ old attractive forces
_________ new attractive forces
The number of new attractive and repulsive forces is same, but the magnitude of attractive forces is more. Thus, when two hydrogen atoms approach each other, the overall potential energy decreases, hence a stable hydrogen molecule is formed.
What is meant by the term bond order? Calculate the bond order of: N2, O2,O2+,and O2-.
Use molecular orbital theory to explain why the Be2 molecule does not exist.
Compare the relative stability of the following species and indicate their magnetic properties:
O2,O2+,O2- (superoxide), O22-(peroxide)
Describe the hybridisation in case of PCl5. Why are the axial bonds longer as compared to equatorial bonds?
Which out of NH3 and NF3 has higher dipole moment and why?
Explain why BeH2 molecule has a zero dipole moment although the Be–H bonds are polar.
Discuss the shape of the following molecules using the VSEPR model:
BeCl2, BCl3, SiCl4, AsF5, H2S, PH3
Write Lewis symbols for the following atoms and ions:
S and S2–; Al and Al3+; H and H–
Describe the change in hybridisation (if any) of the Al atom in the following reaction.
Draw the Lewis structures for the following molecules and ions: H2S, SiCl4, BeF2, , HCOOH
How do you account for the formation of ethane during chlorination of methane?
What are hybridisation states of each carbon atom in the following compounds ?
(i) CH2=C=O,
(ii) CH3CH=CH2,
(iii) (CH3)2CO,
(iv) CH2=CHCN,
(v) C6H6
What will be the minimum pressure required to compress 500 dm3 of air at 1 bar to 200 dm3 at 30°C?
What are the common physical and chemical features of alkali metals?
Calculate the molecular mass of the following:
(i) H2O
(ii) CO2
(iii) CH4
Assign oxidation number to the underlined elements in each of the following species:
(a) NaH2PO4
(b) NaHSO4
(c) H4P2O7
(d) K2MnO4
(e) CaO2
(f) NaBH4
(g) H2S2O7
(h) KAl(SO4)2.12 H2O
What is the basic theme of organisation in the periodic table?
Choose the correct answer. A thermodynamic state function is a quantity
(i) used to determine heat changes
(ii) whose value is independent of path
(iii) used to determine pressure volume work
(iv) whose value depends on temperature only.
A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased.
a) What is the initial effect of the change on vapour pressure?
b) How do rates of evaporation and condensation change initially?
c) What happens when equilibrium is restored finally and what will be the final vapour pressure?
Justify the position of hydrogen in the periodic table on the basis of its electronic configuration.
Calculate the oxidation number of sulphur, chromium and nitrogen in H2SO5, Cr2O2- 7 and NO– 3. Suggest structure of these compounds. Count for the fallacy.
What are the various factors due to which the ionization enthalpy of the main group elements tends to decrease down a group?
Calculate the degree of ionization of 0.05M acetic acid if its pKa value is 4.74.
How is the degree of dissociation affected when its solution also contains (a) 0.01 M (b) 0.1 M in HCl?
Explain what happens when boric acid is heated.
Chlorine is used to purify drinking water. Excess of chlorine is harmful. The excess of chlorine is removed by treating with sulphur dioxide. Present a balanced equation for this redox change taking place in water.
Which of the following reactions will get affected by increasing the pressure?
Also, mention whether change will cause the reaction to go into forward or backward direction.
(i) COCl2 (g) ↔ CO (g) + Cl2 (g)
(ii) CH4 (g) + 2S2 (g) ↔ CS2 (g) + 2H2S (g)
(iii) CO2 (g) + C (s) ↔ 2CO (g)
(iv) 2H2 (g) + CO (g) ↔ CH3OH (g)
(v) CaCO3 (s) ↔ CaO (s) + CO2 (g)
(vi) 4 NH3 (g) + 5O2 (g) ↔ 4NO (g) + 6H2O(g)
Why do elements in the same group have similar physical and chemical properties?
The concentration of hydrogen ion in a sample of soft drink is 3.8 × 10–3 M. what is its pH?
Thermodynamically the most stable form of carbon is
(a) diamond (b) graphite (c) fullerenes (d) coal
Calculate the wavelength, frequency and wave number of a light wave whose period is 2.0 × 10–10 s.
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