Chemistry Test 201

Result

Chemistry Test 201

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Weekly Quiz Competition

Question 1
4 / -1

The half life of a first order reaction is 2000 years. If the concentration after 8000 years is 0.02M, then the initial concentration was:

A
0.04M

B
0.16M

C
0.32M

D
0.08M

Solution
Question 2
4 / -1

For a reaction A → B, enthalpy of reaction is −4.2kJmol⁻¹ and enthalpy of activation is 9.6kJmol⁻¹. The correct potential energy profile for the reaction is shown in option.

A

B

C

D

Solution

ΔH_rxn = (E_a)_f − (E_a)_b

−4.2 = (E_a)_f − (E_a)_b

−4.2 = 9.6 − (E_a)_b

(E_a)_b = 9.6 + 4.2 = 13.8kJmol⁻¹

Since reaction is exothermic, so possible graph is (2) only.

Also (E_a)_f < (E_a)_b, so answer is option (2)
Question 3
4 / -1

The rate constant for a first order reaction is 4.606 × 10⁻³s⁻¹. The time required to reduce 2.0 g of the reactant to 0.2g is:

A
200s

B
500s

C
1000s

D
100s

Solution
Question 4
4 / -1

If the rate constant for a first order reaction is k, the time (t) required for the completion of 99% of the reaction is given by

A
t = 2.303 / k

B
t = 0.693 / k

C
t = 6.909 / k

D
t = 4.606 / k

Solution
Question 5
4 / -1

A first order reaction has a rate constant of 2.303× 10⁻³s⁻¹. The time required for 40gof this reactant to reduce to 10g will be [ Given that log₁₀2 = 0.3010]

A
230.3s

B
301s

C
2000s

D
602s

Solution
Question 6
4 / -1

The correct difference between first and second order reactions is that

A
the rate of a first-order reaction does not depend on reactant concentrations; the rate of a second-order reaction does depend on reactant concentrations

B
the half-life of a first-order reaction does not depend on [A]₀; the half-life of a second-order reaction does depend on [A]₀

C
a first-order reaction can be catalysed; a second-order reaction cannot be catalysed

D
the rate of a first-order reaction does depend on reactant concentrations; the rate of a second-order reaction does not depend on reactant concentrations.

Solution
Question 7
4 / -1

Mechanism of a hypothetical reaction X₂ + Y₂ → 2XY, is given below :

(i) X₂ ⇌ X + X (fast)

(ii) X + Y₂ → XY + Y (slow)

(iii) X + Y → XY (fast)

The overall order of the reaction will be

A
2

B
0

C
1.5

D
1

Solution
Question 8
4 / -1

Rate of a reaction can be defined as

A
the rate of decrease in concentration of any one of the reactants or the rate of increase in concentration of any one of the products

B
the rate of increase in concentration of any one of the products

C
the rate of decrease in concentration of any one of the reactants

D
the sum of rate of decrease in concentration of all the reactants or the rate of increase in concentration of all the products

Solution

This definition captures the change in concentration over time, whether it's a decrease in reactants or an increase in products, reflecting the progress of the chemical reaction. It helps understand how quickly reactants are consumed or products are formed, providing valuable insights into reaction kinetics.
Question 9
4 / -1

Order of reaction can be

A
0

B
integer, fraction, zero

C
whole number

D
fraction

Solution

Order of reaction is equal to the number of moleculi whose concentration is changing with time. It can I zero or in fractions or an integer.
Question 10
4 / -1

The geometry of hydronium ion is

A
tetrahedral

B
linear

C
trigonal pyramidal

D
trigonal planer
Solution
The correct answer is C: trigonal pyramidal.
- The hydronium ion (H₃O⁺) forms when a water molecule (H₂O) gains a proton (H⁺).
- H₂O has a bent structure due to two lone pairs on oxygen, but when it becomes H₃O⁺, one lone pair remains.
- This results in a trigonal pyramidal geometry with three hydrogen atoms and one lone pair on oxygen.
- The bond angles are slightly less than 109.5°, typical of tetrahedral electron pair geometry, but the molecular shape is trigonal pyramidal.