List of top Chemistry Questions asked in CBSE Class XI

Would you expect the first ionization enthalpies for two isotopes of the same element to be the same or different? Justify your answer.

(i) Write the electronic configurations of the following ions: (a) H^– (b) Na⁺ (c) O₂^– (d) F^– 
(ii) What are the atomic numbers of elements whose outermost electrons are represented by (a) 3s¹ (b) 2p³ and (c) 3p⁵? 
(iii) Which atoms are indicated by the following configurations? (a) [He] 2s¹ (b) [Ne] 3s² 3p³ (c) [Ar] 4s² 3d¹.

In the modern periodic table, the period indicates the value of:

Calculate the amount of carbon dioxide that could be produced when 
(i) 1 mole of carbon is burnt in air. 
(ii) 1 mole of carbon is burnt in 16 g of dioxygen. 
(iii) 2 moles of carbon are burnt in 16 g of dioxygen.

The total number of protons in $ 10\,g$ of calcium carbonate is $ (N_{0}=6.023\times 10^{23})$ :

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.

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.

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.

Explain why the following systems are not aromatic?

Match the following prefixes with their multiples:

S.No	Prefixes	Multiples
(i)	micro	106
(ii)	deca	109
(iii)	mega	10–6
(iv)	giga	10–15
(v)	femto	10

The ionization constant of benzoic acid is 6.46 × 10^–5 and K_sp for silver benzoate is 2.5 × 10^–13. How many times is silver benzoate more soluble in a buffer of pH 3.19 compared to its solubility in pure water?

What sorts of information can you draw from the following reaction?
(CN)₂( g)+2OH⁻(aq)\(\rightarrow\)CN⁻(2aq)+CNO⁻(aq)+H₂O(l)

The solubility product constant of Ag₂CrO₄ and AgBr are 1.1×10^–12 and 5.0×10^–13 respectively. Calculate the ratio of the molarities of their saturated solutions.

Balance the following redox reactions by ion-electron method: 
(a)MnO₄^- _(aq) + I ^- _(aq) → MnO_2(s) + I₂(s) (in basic medium)
(b) MnO₄^- _(aq) + SO_2(g) → Mn₂⁺_(aq) +HSO₄^- _(aq) (in acidic solution)
(c) H₂O_2(aq)+Fe₂⁺_(aq) → Fe₃⁺ _(aq) + H₂O (l) (in acidic solution)
(d) Cr₂O₇^2-+ SO_2(g) → Cr³⁺ _(aq) +SO₄^2- _(aq) (in acidic solution)

Which of the following carbocation is most stable?

Determine the molecular formula of an oxide of iron, in which the mass per cent of iron and oxygen are 69.9 and 30.1, respectively.

Explain the principle of paper chromatography.

Discuss the chemistry of Lassaigne’s test.

Why is Wurtz reaction not preferred for the preparation of alkanes containing odd number of carbon atoms? Illustrate your answer by taking one example

Calculate the entropy change in surroundings when \(1.00\ mol\) of \(H_2O(l)\) is formed under standard conditions. \(∆_fH^Θ= –286\ kJ mol^{-1}\).

Comment on the thermodynamic stability of \(NO(g)\), given
\(\frac 12N_2(g) +\frac 12O_2(g)→NO(g); \ \ \ \ ∆_rH^Θ= 90\ kJ mol^{-1}\)
\(NO(g) +\frac 12 O_2(g)→NO_2(g);\ \ \  ∆_rH^Θ= –74\ kJ mol^{-1}\)

The equilibrium constant for a reaction is \(10\). What will be the value of \(∆G^Θ\)?
\(R= 8.314\ JK^{-1} mol^{-1}, T=300\ K\)

For the reaction
\(2A(g)+B(g)→2D(g)\)
\(∆U^Θ= -10.5\ kJ\) and \(∆S^Θ= -44.1\ JK^{-1}\).
Calculate \(∆G^Θ\) for the reaction, and predict whether the reaction may occur spontaneously.

For the reaction, \(2Cl(g)→Cl_2(g)\), what are the signs of \(∆H\) and \(∆S\) ?

For the reaction at \(298\ K\),
\(2A+B→C\)
\(∆H = 400\ kJ mol^{-1}\) and \(∆S = 0.2\ kJ K^{-1} mol^{-1}\)
At what temperature will the reaction become spontaneous considering \(∆H\) and \(∆S\) to be constant over the temperature range.