List of top Chemistry Questions

Which of the following statements related to the modern periodic table is incorrect?

What is K_c for the following equilibrium when the equilibrium concentration of each substance is: [SO₂]= 0.60 M, [O₂] = 0.82 M and [SO₃] = 1.90 M ?
\(2SO_2(g) + O_2(g) ⇋ 2SO_3(g)\)

Which one of the following statements is incorrect in relation to ionization enthalpy?

Considering the elements B, Al, Mg, and K, the correct order of their metallic character is:

Considering the elements B, C, N, F, and Si, the correct order of their non-metallic character is:

At a certain temperature and total pressure of 10⁵ Pa, iodine vapour contains 40% by volume of \(\text {I}\) atoms
\( I_2 (g) ⇋ 2I (g)\)
Calculate K_p for the equilibrium.

Considering the elements F, Cl, O and N, the correct order of their chemical reactivity in terms of oxidizing property is:

Write the expression for the equilibrium constant, K_c for each of the following reactions: 

1. \(2NOCl (g) ⇋ 2NO (g) + Cl_2 (g)\)
2. \(2Cu(NO_3)_2 (s) ⇋ 2CuO (s) + 4NO_2 (g) + O_2 (g)\)
3. \(CH_3COOC_2H_5(aq) + H_2O(l) ⇋ CH_3COOH (aq) + C_2H_5OH (aq)\)
4. \(Fe^{3+} (aq) + 3OH^– (aq) ⇋ Fe(OH)_3 (s)\)
5. \(I_2 (s) + 5F_2 ⇋ 2IF_5\)

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.