WILLER ACADEMY

Monthly Assessment Test

Class 12th (Science)

Subject Chemistry

Duration 90 Minutes

Max Marks 50

📋 Instructions

• This test contains 20 numerical problems - 10 from Solid State and 10 from Chemical Kinetics.
• All questions are compulsory. Each question carries 2.5 marks.
• Show all necessary calculations. Answers without proper working will not be awarded full marks.
• Use the provided boxes to write your final answer with appropriate units.
• Non-programmable calculators are permitted.

Chapter 1: Solid State

Question 1

2.5 Marks

A compound forms a hexagonal close-packed structure. What is the total number of voids in 0.5 mol of it? How many of these are tetrahedral voids?

Answer:

Question 2

2.5 Marks

An element has a body-centered cubic structure with a cell edge of 288 pm. The density of the element is 7.2 g/cm³. Calculate the number of atoms present in 200 g of the element.

Answer:

Question 3

2.5 Marks

A compound made of elements A and B crystallizes in a cubic structure. Atoms A are present at the corners and atoms B at the body center. What is the formula of the compound?

Answer:

Question 4

2.5 Marks

Copper crystallizes into a face-centered cubic lattice and has a density of 8.93 g/cm³. Calculate the radius of the copper atom. (Atomic mass of Cu = 63.55 g/mol)

Answer:

Question 5

2.5 Marks

A unit cell of sodium chloride has four formula units. The edge length of the unit cell is 0.564 nm. Calculate the density of sodium chloride. (Na = 23 g/mol, Cl = 35.5 g/mol)

Answer:

Question 6

2.5 Marks

An element crystallizes in a structure having a fcc unit cell of an edge 200 pm. Calculate its density if 200 g of this element contains 24 × 10²³ atoms.

Answer:

Question 7

2.5 Marks

Analysis shows that nickel oxide has formula Ni_0.98O. What fraction of nickel exists as Ni³⁺ ions?

Answer:

Question 8

2.5 Marks

A compound forms hexagonal close-packed structure. What is the total number of voids in 0.8 mol of it? How many of these are octahedral voids?

Answer:

Question 9

2.5 Marks

The density of KBr is 2.75 g/cm³. The length of the unit cell is 654 pm. Predict the type of lattice (fcc). (Atomic masses: K = 39, Br = 80)

Answer:

Question 10

2.5 Marks

An element with molar mass 27 g/mol forms a cubic unit cell with edge length 4.05 × 10⁻⁸ cm. If its density is 2.7 g/cm³, what is the nature of the cubic unit cell?

Answer:

Chapter 2: Chemical Kinetics

Question 11

2.5 Marks

The decomposition of N₂O₅ is given by the equation:
2N₂O₅ → 4NO₂ + O₂
If the rate constant is 3.0 × 10⁻⁴ s⁻¹, what is the half-life of the reaction?

Answer:

Question 12

2.5 Marks

The rate constant for a first-order reaction is 60 s⁻¹. How much time will it take to reduce the initial concentration of the reactant to its 1/16th value?

Answer:

Question 13

2.5 Marks

For a reaction A + B → Products, the rate law is given by r = k[A]¹/²[B]². What is the order of the reaction?

Answer:

Question 14

2.5 Marks

The half-life for radioactive decay of ¹⁴C is 5730 years. An archaeological artifact containing wood had only 80% of the ¹⁴C found in a living tree. Estimate the age of the artifact.

Answer:

Question 15

2.5 Marks

The rate constant of a reaction at 500K is 1.6 × 10⁶ s⁻¹ and at 700K is 6.36 × 10⁷ s⁻¹. Calculate the activation energy of the reaction.

Answer:

Question 16

2.5 Marks

A first-order reaction takes 40 minutes for 30% decomposition. Calculate t_1/2.

Answer:

Question 17

2.5 Marks

The rate constant for the decomposition of hydrocarbons is 2.418 × 10⁻⁵ s⁻¹ at 546 K. If the energy of activation is 179.9 kJ/mol, what will be the value of pre-exponential factor?

Answer:

Question 18

2.5 Marks

For the reaction 2A + B → C, the initial rate was measured at several different concentrations of A and B. Determine the rate law and the value of the rate constant.
[A] (M)    [B] (M)    Initial Rate (M/s)
0.05        0.05        0.035
0.10        0.05        0.070
0.20        0.10        0.56

Answer:

Question 19

2.5 Marks

The decomposition of NH₃ on platinum surface is zero order reaction. What are the rates of production of N₂ and H₂ if k = 2.5 × 10⁻⁴ mol L⁻¹ s⁻¹?

Answer:

Question 20

2.5 Marks

The rate constant for a reaction is 1.2 × 10⁻² s⁻¹ at 300 K and 4.2 × 10⁻² s⁻¹ at 320 K. Calculate the activation energy of the reaction.

Answer:

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