List of top Chemistry Questions asked in CBSE Class XI

The reaction of cyanamide, $NH_2CN(s)$, with dioxygen was carried out in a bomb calorimeter, and $∆U$ was found to be $–742.7\ kJ\ mol^{–1}$ at $298\ K$. Calculate enthalpy change for the reaction at $298\ K$.
$NH_2CN(g)+\frac 32O_2(g)→N_2(g)+CO_2(g)+H_2O(l)$

In a process, 701 J of heat is absorbed by a system and 394 J of work is done by the system. What is the change in internal energy for the process?

A reaction, $A+B→C+D+q$ is found to have a positive entropy change. The reaction will be

$∆U^Θ$ of combustion of methane is – $X\ kJ \ mol^{–1}$. The value of $∆H^Θ$ is

The enthalpies of all elements in their standard states are:

For the process to occur under adiabatic conditions, the correct condition is:

Assign oxidation numbers to the underlined elements in each of the following species: 

1. $NaH_2\underline PO_4$ 
2. $NaH\underline SO_4$ 
3. $H_4\underline P_2O_7$ 
4. $K_2\underline {Mn}O_4$ 
5. $Ca\underline O_2$ 
6. $Na\underline BH_4$ 
7. $H_2\underline S_2O_7$ 
8. $KAl(\underline SO_4)_2.12 H_2O$

Choose the correct answer. A thermodynamic state function is a quantity

A sample of 0.50 g of an organic compound was treated according to Kjeldahl’s method. The ammonia evolved was absorbed in 50 ml of 0.5 M H₂SO₄. The residual acid required 60 mL of 0.5 M solution of NaOH for neutralization. Find the percentage composition of nitrogen in the compound.

Explain why alkyl groups act as electron donors when attached to a $\pi$ system.

Identify the functional groups in the following compounds.

Give condensed and bond line structural formulas and identify the functional group(s) present, if any, for, 

1. 2,2,4-Trimethylpentane, 
2. 2-Hydroxy-1,2,3-propanetricarboxylic acid, 
3.  Hexanedial.

An organic compound contains 69% carbon and 4.8% hydrogen, the remainder being oxygen. Calculate the masses of carbon dioxide and water produced when 0.20 g of this substance is subjected to complete combustion.

The reaction, $CO(g) + 3H_2(g) \leftrightarrow CH_4(g) + H_2O(g)$ is at equilibrium at 1300 K in a 1L flask. It also contain 0.30 mol of CO, 0.10 mol of $H_2$ and 0.02 mol of $H_2O$ and an unknown amount of $CH_4$ in the flask. Determine the concentration of $CH_4$ in the mixture. The equilibrium constant, $K_c$ for the reaction at the given temperature is 3.90.

Why is it necessary to use acetic acid and not sulphuric acid for acidification of sodium extract for testing sulphur by lead acetate test?

Why is a solution of potassium hydroxide used to absorb carbon dioxide evolved during the estimation of carbon present in an organic compound?

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 $O_3$?

What are hybridization states of each carbon atom in the following compounds? 
$CH_2=C=O,\, CH_3CH=CH_2$,$(CH_3)_2CO, \,CH_2=CHCN, \,C_6H_6.$

Will CCl₄ give white precipitate of AgCl on heating it with silver nitrate? Give reason for your answer.

Explain, why an organic liquid vaporises at a temperature below its boiling point in its steam distillation ?

Name a suitable technique of separation of the components from a mixture of calcium sulphate and camphor.

Considering x-axis as the internuclear axis which out of the following will not form a sigma bond and why?

Explain the reason for the fusion of an organic compound with metallic sodium for testing nitrogen, sulphur and halogens.

Why is nitric acid added to sodium extract before adding silver nitrate for testing halogens?

Write Lewis symbols for the following atoms and ions: $S$ and $S ^{2-}$ ; $Al$ and $Al ^{3+}$ ; $H$ and $H ^-$