Engineering Chemistry MCQ (Laws of Photochemistry)

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Engineering Chemistry MCQ (Laws of Photochemistry)

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Laws of Photochemistry

1. __________ is also known as the Principle of Photochemical Activation.
a) Grothus–Draper law
b) Lambert’s law
c) Draper law
d) Stark law
Answer: a
Explanation: Grothus–Draper law is also known as the Principle of Photochemical
Activation. This law states that only that light which is absorbed by a system is
responsible for doing a photochemical change.

2. The absorbed radiation does not necessarily cause a chemical reaction.
a) True
b) False
Answer: a
Explanation: Yes, the absorbed radiation does not necessarily cause a chemical
reaction. If the environment is not conducive for the molecules to react, then the
light energy will remain unused or in some cases may be re-emitted as heat or light.

3. When a beam of light is allowed to pass through a transparent medium, the rate of decrease of intensity with the thickness of medium is __________ to the intensity of the light.
a) inversely proportional
b) directly proportional
c) equal
d) not related
Answer: b
Explanation: As per Lambert’s law, when a beam of light passes through a
transparent medium, the rate of decrease of intensity with the thickness of medium
is directly proportional to the intensity of the light. Mathematically, it may be stated
as follows: -dI/t=kI.

4. The intensity of a beam of monochromatic light ___________ with the increase in the concentration of the absorbing substance arithmetically.
a) decrease exponentially
b) increase exponentially
c) decrease linearly
d) increase linearly
Answer: a
Explanation: As per Beer’s Law, the intensity of incident light decreases
exponentially with the increase in concentration of the absorbing substance
arithmetically. Mathematically, it is shown as follows: I = Io/ekc.

5. __________ is also known as Principle of Quantum Activation.
a) Lambert’s law
b) Beer’s law
c) Stark-Einstein law
d) Stark law
Answer: c
Explanation: Stark-Einstein law is also known as the Principle of Quantum Activation.
It states that in a primary photochemical process, only one molecule is activated for
every photo of light absorbed by the chemical system.

6. When a molecule absorbs a photon, it is necessary that only one molecule should react.
a) True
b) False
Answer: b
Explanation: When a molecule absorbs a photon, it is not necessary that only one
molecule should react. It may or may not react or may cause the reaction of many
molecules through a chain mechanism.

7. Beer-Lambert law is applicable if ____________
a) temperature changes
b) dilute solution is used
c) non-monochromatic radiation is used
d) temperature varies linearly
Answer: b
Explanation: Beer-Lambert law is not applicable if temperature changes during
measurements. It is also not applicable if non-monochromatic radiation is used. It is
applicable only to dilute solutions.

8. When light falls on a cell containing a reaction mixture __________ component of light is responsible for producing chemical reaction.
a) absorbed
b) adsorbed
c) transmitted
d) reflected
Answer: a
Explanation: When light falls on a cell containing a reaction mixture, some light is
absorbed and the remaining light is transmitted. Transmitted light is chemically
ineffective whereas absorbed component of light is capable of producing chemical reaction.

9. Grothus – Draper law is __________ in nature.
a) purely qualitative
b) quantitative
c) qualitative and quantitative
d) non-acceptable
Answer: a
Explanation: Grothus – Draper law is qualitative in nature. It does not give us any
idea about the relation between absorbed radiations and molecules undergoing change.

10. Stark-Einstein studied the __________ aspects of photochemical reactions by application of quantum theory of light.
a) qualitative
b) quantitative
c) geometrical
d) qualitative and quantitative
Answer: b
Explanation: Stark-Einstein studied the quantitative aspects of photochemical
reactions by application of the quantum theory of light. They observed that each
molecule taking part in the reaction absorbs only one photon of light.