List of top Chemistry Questions asked in CBSE Class XI

Dihydrogen gas used in Haber’s process is produced by reacting methane from natural gas with high temperature steam. The first stage of two stage reaction involves the formation of CO and H₂. In second stage, CO formed in first stage is reacted with more steam in water gas shift reaction,
\(CO (g) + H_2O (g) ⇋ CO_2 (g) +H_2 (g)\)
If a reaction vessel at 400°C is charged with an equimolar mixture of CO and steam such that \(P_{co}= P_{H_2O} = 4.0\) bar, what will be the partial pressure of H₂ at equilibrium? K_p= 10.1 at 400°C.

The ionization constant of phenol is 1.0 × 10^–10. What is the concentration of phenolate ion in a 0.05 M solution of phenol? What will be its degree of ionization if the solution is also 0.01M in sodium phenolate?

At 473 K, equilibrium constant K_c for decomposition of phosphorus pentachloride, PCl₅ is \(8.3 ×10^{-3}\). If decomposition is depicted as,
\(PCl_5 (g) ⇋ PCl_3 (g) + Cl_2 (g)\)   \(∆_r H^Θ = 124.0\  kJ mol^{–1}\)

1. write an expression for K_c for the reaction.
2. what is the value of K_c for the reverse reaction at the same temperature?

1. what would be the effect on K_c if
   1. more PCl₅ is added
   2. pressure is increased
   3. the temperature is increased ?

The ionization constant of HF, HCOOH and HCN at 298K are 6.8×10^–4,1.8×10^–4 and 4.8×10^–9 respectively. Calculate the ionization constants of the corresponding conjugate base.

The pH of a sample of vinegar is 3.76. Calculate the concentration of hydrogen ions in it.

The concentration of hydrogen ions in a sample of soft drink is 3.8 × 10^–3 M. What is its pH?

Classify the following species into Lewis acids and Lewis bases and show how these act as Lewis acid/base: (a) OH^– (b) F^– (c) H⁺ (d) BCl₃

Describe the effect of: 

1. addition of H₂
2. addition of CH₃OH
3. removal of CO
4. removal of CH₃OH 

on the equilibrium of the reaction:
\(2H_2(g) + CO (g) ⇋ CH_3OH (g)\)

The species: H₂O, HCO₃^–, HSO₄^– and NH₃ can act both as Brönsted acids and bases. For each case give the corresponding conjugate acid and base.

Write the conjugate acids for the following Brönsted bases: NH₂^–, NH₃ and HCOO^–.

What will be the conjugate bases for the Brönsted acids: HF, H₂SO₄ and HCO₃^–?

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 K_p for the above reaction.
2. How will the values of K_p and composition of equilibrium mixture be affected by
   1. increasing the pressure
   2. increasing the temperature
   3. using a catalyst?

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. \(4NH_3 (g) + 5O_2 (g) ⇋ 4NO (g) + 6H_2O(g)\)

Which of the following are Lewis acids? H₂O, BF₃, H⁺, and NH₄⁺.

What effect does branching of an alkane chain has on its boiling point?

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^–

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 are the necessary conditions for any system to be aromatic?

Calculate:

1. ∆G^Θ 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,
 ∆_fG^Θ (NO₂) = 52.0 kJ/mol
∆_fG^Θ (NO) = 87.0 kJ/mol
∆_fG^Θ (O₂) = 0 kJ/mol.

How do you account for the formation of ethane during chlorination of methane?

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 K_c for this reaction at the above temperature.

Bromine monochloride, BrCl decomposes into bromine and chlorine and reaches the equilibrium:
\(2BrCl (g) ⇋ Br_2 (g) + Cl_2 (g)\)
for which K_c = 32 at 500 K. If initially pure BrCl is present at a concentration of 3.3 × 10^–3 mol L^–1, what is its molar concentration in the mixture at equilibrium?

What is meant by the term bond order? Calculate the bond order of: \(N_2\), \(O_2\), \(O_2^+\) and \(O_2^-\) .

Equilibrium constant, K_c for the reaction
\(N_2 (g) + 3H_2 (g) ⇋ 2NH_3 (g)\)
At 500 K is 0.061 At a particular time, the analysis shows that composition of the reaction mixture is 3.0 mol L^–1 N₂, 2.0 mol L^–1 H₂ and 0.5 mol L^–1 NH₃. Is the reaction at equilibrium? If not in which direction does the reaction tend to proceed to reach equilibrium?

One of the reaction that takes place in producing steel from iron ore is the reduction of iron(II) oxide by carbon monoxide to give iron metal and CO₂.
\(FeO (s) + CO (g) ⇋ Fe (s) + CO_2 (g);\ K_p = 0.265\  \text {atm}\) at 1050 K
What are the equilibrium partial pressures of CO and CO₂ at 1050 K if the initial partial pressures are: \(P_{CO}\) = 1.4 atm and \(P_{CO_2}\) = 0.80 atm?