List of top Chemistry Questions

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.

In terms of period and group where would you locate the element with Z =114?

Write the atomic number of the element present in the third period and seventeenth group of the periodic table.

Which element do you think would have been named by
(i) Lawrence Berkeley Laboratory
(ii) Seaborg's group?

Why do elements in the same group have similar physical and chemical properties?

What does atomic radius and ionic radius really mean to you?

How does atomic radius vary in a period and in a group? How do you explain the variation?

What do you understand by isoelectronic species? Name a species that will be isoelectronic with each of the following atoms or ions. 

1. F^- 
2. Ar 
3. Mg²⁺ 
4. Rb⁺

Consider the following species: N^3- , O^2-, F^-, Na⁺, Mg²⁺ and Al³⁺ 

1. What is common in them? 
2. Arrange them in the order of increasing ionic radii.

Explain why cations are smaller and anions larger in radii than their parent atoms?

Anything that influences the valence electrons will affect the chemistry of the element. Which one of the following factors does not affect the valence shell?

What are the various factors due to which the ionization enthalpy of the main group elements tends to decrease down a group?

The first ionization enthalpy values (in kJmol^-1 ) of group 13 elements are :

B	Al	Ga	In	Tl
801	577	579	558	589

How would you explain this deviation from the general trend?

Which of the following pairs of elements would have a more negative electron gain enthalpy? 

1. O or F 
2. F or Cl

Dinitrogen and dihydrogen react with each other to produce ammonia according to the following chemical equation: \(N_2 (g) + H_2 (g) → 2NH_3 (g)\)

1. Calculate the mass of ammonia produced if 2.00 × 10³ g dinitrogen reacts with 1.00 × 10³ g of dihydrogen.
2. Will any of the two reactants remain unreacted?
3. If yes, which one and what would be its mass?

How are 0.50 mol Na₂CO₃ and 0.50 M Na₂CO₃ different?

If 10 volumes of dihydrogen gas reacts with five volumes of dioxygen gas, how many volumes of water vapour would be produced?