List of top Chemistry Questions

Define octet rule. Write its significance and limitations.

Discuss the shape of the following molecules using the VSEPR model: 
BeCl₂, BCl₃, SiCl₄, AsF₅, H₂S, PH₃

Although geometries of NH₃ and H₂O molecules are distorted tetrahedral, bond angle in water is less than that of ammonia. Discuss.

Explain the important aspects of resonance with reference to the \(CO_3^{2-}\) ion.

H₃PO₃ can be represented by structures 1 and 2 shown below. Can these two structures be taken as the canonical forms of the resonance hybrid representing H₃PO₃ ? If not, give reasons for the same.

Find out the value of \(K_c\) for each of the following equilibria from the value of \(K_p\): 

1. \(2NOCl (g) ⇋ 2NO (g) + Cl_2 (g); \ K_p= 1.8 × 10^{–2}\  at \ 500\ K\)
2. \(CaCO_3 (s) ⇋ CaO(s) + CO_2(g); \ K_p= 167 \ at \ 1073\  K\)

Use Lewis symbols to show electron transfer between the following atoms to form cations and anions:

1. K and S 
2. Ca and O 
3. Al and N.

Write the significance/applications of dipole moment.

Define electronegativity. How does it differ from electron gain enthalpy?

Arrange the bonds in order of increasing ionic character in the molecules: LiF, K₂O, N₂, SO₂ and ClF₃.

The skeletal structure of CH₃COOH as shown below is correct, but some of the bonds are shown incorrectly. Write the correct Lewis structure for acetic acid.

For the following equilibrium, \(K_c = 6.3 × 10^{14}\) at \(1000\  K\)
\(NO (g) + O_3 (g) ⇋ NO_2 (g) + O_2 (g)\)
Both the forward and reverse reactions in the equilibrium are elementary bimolecular reactions. What is \(K'_c\) for the reverse reaction?

Explain why pure liquids and solids can be ignored while writing the equilibrium constant expression?

Reaction between \(N_2\) and \(O_2^–\) takes place as follows: 
\(2N_2 (g) + O_2 (g) ⇋ 2N_2O (g)\)
If a mixture of \(0.482 \ mol\) \(N_2\) and \(0.933\  mol\) of \(O_2\) is placed in a \(10\  L\) reaction vessel and allowed to form \(N_2O\) at a temperature for which \(K_c = 2.0 × 10^{–37}\), determine the composition of equilibrium mixture.

In astronomical observations, signals observed from the distant stars are generally weak. If the photon detector receives a total of 3.15 × 10^–18 J from the radiations of 600 nm, calculate the number of photons received by the detector.

Lifetimes of the molecules in the excited states are often measured by using pulsed radiation source of duration nearly in the nano-second range. If the radiation source has a duration of 2 ns and the number of photons emitted during the pulse source is 2.5 × 10¹⁵, calculate the energy of the source.

The longest wavelength doublet absorption transition is observed at 589 and 589.6 nm. Calculate the frequency of each transition and energy difference between two excited states.

The work function for caesium atom is 1.9 eV. Calculate (a) the threshold wavelength and (b) the threshold frequency of the radiation. If the caesium element is irradiated with a wavelength 500 nm, calculate the kinetic energy and the velocity of the ejected photoelectron.

Nitric oxide reacts with Br₂ and gives nitrosyl bromide as per reaction given below:
\(2NO (g) + Br_2 (g) ⇋ 2NOBr (g)\)
When 0.087 mol of NO and 0.0437 mol of Br₂ are mixed in a closed container at constant temperature, 0.0518 mol of NOBr is obtained at equilibrium. Calculate equilibrium amount of NO and Br₂ .

Which out of NH₃ and NF₃ has higher dipole moment and why?

At \(450\ K\), \(K_p= 2.0 × 10^{10}/bar\) for the given reaction at equilibrium.
\(2SO_2(g) + O_2(g) ⇋ 2SO_3 (g)\)
What is \(K_c\) at this temperature ?

What is the basic theme of organisation in the periodic table?

Which important property did Mendeleev use to classify the elements in his periodic table and did he stick to that? 

What is the basic difference in approach between the Mendeleev's Periodic Law and the Modern Periodic Law?

On the basis of quantum numbers, justify that the sixth period of the periodic table should have 32 elements.