List of top Chemistry Questions asked in CBSE Class XI

At 1127 K and 1 atm pressure, a gaseous mixture of CO and CO2 in equilibrium with soild carbon has 90.55% CO by mass
\(C(s) + CO_2(g) ⇋ 2CO(g)\)
Calculate Kc for this reaction at the above temperature.
How do you account for the formation of ethane during chlorination of methane?
Calculate:
  1. ∆GΘ and 
  2. the equilibrium constant for the formation of NO2 from NO and O2 at 298 K
\(NO (g) + \frac 12O_2 (g) ⇋ NO_2 (g)\)
where,
 ∆fGΘ (NO2) = 52.0 kJ/mol
∆fGΘ (NO) = 87.0 kJ/mol
∆fGΘ (O2) = 0 kJ/mol.
What are the necessary conditions for any system to be aromatic?
Does the number of moles of reaction products increase, decrease or remain same when each of the following equilibria is subjected to a decrease in pressure by increasing the volume?
  1. \(PCl_5 (g) ⇋ PCl_3 (g) + Cl_2 (g)\)
  2. \(CaO (s) + CO_2 (g) ⇋ CaCO_3 (s)\)
  3. \(3Fe (s) + 4H_2O (g) ⇋ Fe_3O_4 (s) + 4H_2 (g)\)
In the alkane \( H_3C-CH_2-C(CH_3)_2-CH_2-CH(CH_3)_2\) , identify 1°,2°,3° carbon atoms and give the number of H atoms bonded to each one of these.
What is meant by the conjugate acid-base pair? Find the conjugate acid/base for the following species: HNO2, CN– , HClO4,F–,OH–,CO and S2–
What effect does branching of an alkane chain has on its boiling point?
Which of the following are Lewis acids? H2O, BF3, H+, and NH4+.
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.
  1. \(COCl_2 (g) ⇋ CO (g) + Cl_2 (g)\)
  2. \(CH_4 (g) + 2S_2 (g) ⇋ CS_2 (g) + 2H_2S (g)\)
  3. \(CO_2 (g) + C (s) ⇋ 2CO (g)\)
  4. \(2H_2 (g) + CO (g) ⇋ CH_3OH (g)\)
  5. \(CaCO_3 (s) ⇋ CaO (s) + CO_2 (g)\)
  6. \(4NH_3 (g) + 5O_2 (g) ⇋ 4NO (g) + 6H_2O(g)\)
Dihydrogen gas is obtained from natural gas by partial oxidation with steam as per following endothermic reaction:
\(CH_4 (g) + H_2O (g) ⇋ CO (g) + 3H_2 (g)\)
  1. Write as expression for Kp for the above reaction.
  2. How will the values of Kp and composition of equilibrium mixture be affected by
    1. increasing the pressure
    2. increasing the temperature
    3. using a catalyst?
Explain the reason for the fusion of an organic compound with metallic sodium for testing nitrogen, sulphur and halogens.
Considering x-axis as the internuclear axis which out of the following will not form a sigma bond and why?
Why is nitric acid added to sodium extract before adding silver nitrate for testing halogens?
Name a suitable technique of separation of the components from a mixture of calcium sulphate and camphor.
Explain, why an organic liquid vaporises at a temperature below its boiling point in its steam distillation ?
Will CCl4 give white precipitate of AgCl on heating it with silver nitrate? Give reason for your answer.
The value of \(K_c\) for the reaction  \(3O_2 \,(g) \leftrightarrow 2O_3 \,(g)\) is \(2.0 ×10^{–50}\) at 25°C. If the equilibrium concentration of \(O_2\) in air at 25°C is \(1.6 ×10^{–2}\), what is the concentration of \(O_3\)?
Why is a solution of potassium hydroxide used to absorb carbon dioxide evolved during the estimation of carbon present in an organic compound?
Write Lewis symbols for the following atoms and ions: \(S\) and \(S ^{2-}\) ; \(Al\) and \(Al ^{3+}\) ; \(H\) and \(H ^-\)
Discuss the principle of estimation of halogens, sulphur and phosphorus present in an organic compound.
The following data are obtained when dinitrogen and dioxygen react together to form different compounds: 
          Mass of dinitrogen                Mass of dioxygen 
(i)              14 g                                            16 g 
(ii)             14 g                                             32 g 
(iii)            28 g                                             32 g 
(iv)            28 g                                             80 g 
  1. Which law of chemical combination is obeyed by the above experimental data? Give its statement.
  2. Fill in the blanks in the following conversions: 
    (i)1 km = ...................... mm = ...................... pm 
    (ii) 1 mg = ...................... kg = ...................... ng 
    (iii) 1 mL = ...................... L = ...................... dm3
A sample of drinking water was found to be severely contaminated with chloroform, CHCl3, supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass).
  1. Express this in per cent by mass.
  2. Determine the molality of chloroform in the water sample.
What is the concentration of sugar (C12H22O11) in mol L–1 if its 20 g are dissolved in enough water to make a final volume up to 2L?
A reaction, \(A+B→C+D+q\) is found to have a positive entropy change. The reaction will be