Engineering Chemistry MCQ (Photochemical Reactions)
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1. The reactions which are caused by heat and in absence of light is called _____
a) Photochemical reactions
b) Dark reactions
c) Reversible reaction
d) Reversible photochemical reaction
Explanation: The reactions which are caused by heat and in absence of light are
called thermal or dark reactions. A reaction that takes place by absorption of light
radiations of a specific wavelength is called photochemical reaction.
2. In photochemical reactions, absorption of _____ radiations takes place.
a) ultraviolet and visible
c) only visible
d) visible and x-rays
Explanation: Absorption of visible and ultraviolet radiations can only take place in a
photochemical reaction. Wavelength of absprbed radiations ranges from 2000 –8000 Å.
3. In photochemical reactions, the presence of light is not required for the reaction to take place.
Explanation: In photochemical reactions, presence of light is the primary
requirement for the reaction to take place. It involves absorption of light radiations.
4. Ozone is formed by ______ dissociation of molecular oxygen into individual oxygen atoms.
Explanation: Molecular oxygen undergoes photochemical dissociation into
individual oxygen atoms. These oxygen atoms are reacted with molecular oxygen to form ozone.
5. Which of the following is an example of photochemical reaction?
b) Decomposition of ammonia
c) Formation of NaOH
d) Decomposition of HCl
Explanation: Photosynthesis is an example of photochemical reaction. In
photosynthesis, light energy is captured by the chlorophyll present in the thylakoids
of the chloroplast for the production of photons. Water is splitted by photons from
light energy and it enables ATP production that drives the entire process.
6. Which of the following are the principle laws of photochemistry?
a) Grothus-Draper and Stark-Einstein law
b) Raoult’s and Dalton’s law
c) Raoult’s and Henry’s law
d) Lambert’s and Beer’s law
Explanation: Two fundamental principles of photochemistry are there. They are
Grothus-Draper law and Stark-Einstein law.
7. Mercaptans can be produced by photochemical addition of ______ to alpha olefins.
a) hydrogen sulphide
Explanation: Mercaptans can be produced by photochemical addition of hydrogen
sulfide to alpha olefins. In this method, there is a provision for increasing the total
conversion of reactants to mercaptans by including carbon disulfide in the reaction mixture.
8. Vision is initiated by a photochemical reaction of ______
b) Hydrogen Chloride
Explanation: Vision is initiated by a photochemical reaction of rhodopsin. It is the
primary photoreceptor molecule of vision.
9. Medicine bottles are often made with darkened glass _______
a) to prevent the drug from photodegradation
b) to allow the photodegradation of drug
c) to reduce the cost
d) to allow oxidation of drug
Explanation: Medicine bottles are often made with darkened glass to prevent the
drugs from photodegradation. Generally, brown color is used because of its ability
to prevent UV light from degrading the potentially photosensitive contents through photochemical reactions.
10. In _____ reactions, molecules absorbing light do not themselves react but induce other molecules to react.
Explanation: The reactions in which molecules absorbing light do not themselves
react but induce other molecules to react are called photosensitized reactions. The
reactions which are caused by heat and in absence of light is called thermal or dark reactions.