Assertion (A): Adsorption is a surface phenomenon. Reason (R): Adsorption occurs when molecules adhere to the surface of a solid or liquid.
Options:
Answer: (1)
Explanation: Adsorption is indeed a surface phenomenon, and the
reason explains why adsorption happens at the surface of a solid or liquid.
Assertion (A): Adsorption increases with an increase in pressure. Reason (R): With increased pressure, the concentration of gas molecules increases, leading to higher adsorption on the solid surface.
Options:
Answer: (1)
Explanation: Adsorption increases with increased pressure, as
more molecules come into contact with the surface, leading to more adsorption.
Assertion (A): Physical adsorption is reversible. Reason (R): Physical adsorption involves weak forces such as van der Waals forces, which can be overcome by changing the temperature or pressure.
Options:
Answer: (1)
Explanation: Physical adsorption is reversible because the weak
forces involved can be easily broken by changing temperature or pressure.
Assertion (A): Chemisorption is an irreversible process. Reason (R): Chemisorption involves the formation of strong chemical bonds between the adsorbate and the adsorbent.
Options:
Answer: (1)
Explanation: Chemisorption is irreversible because strong
chemical bonds are formed, making desorption difficult.
Assertion (A): Adsorption is always exothermic. Reason (R): During adsorption, the adsorbate molecules release energy as they form bonds with the surface of the adsorbent.
Options:
Answer: (1)
Explanation: Adsorption is an exothermic process because energy
is released when adsorbate molecules bind to the surface of the adsorbent.
Assertion (A): The adsorption of gases on solids generally increases with increasing temperature. Reason (R): Adsorption is an exothermic process, so higher temperatures reduce adsorption.
Options:
Answer: (4)
Explanation: The adsorption of gases generally decreases with
increasing temperature because adsorption is exothermic, and higher temperatures
favor desorption.
Assertion (A): Adsorption is used in gas purification. Reason (R): Adsorption removes impurities from gases by trapping them on the surface of an adsorbent.
Options:
Answer: (1)
Explanation: Adsorption is effectively used in gas purification
processes, such as removing harmful gases from air using activated charcoal.
Assertion (A): The extent of adsorption depends on the surface area of the adsorbent. Reason (R): A larger surface area provides more sites for the adsorbate molecules, leading to more adsorption.
Options:
Answer: (1)
Explanation: A larger surface area allows for more molecules to
be adsorbed, as more surface sites are available for interaction.
Assertion (A): Adsorption leads to an increase in entropy. Reason (R): The adsorbate molecules become more ordered as they are adsorbed on the surface of the adsorbent.
Options:
Answer: (3)
Explanation: Adsorption results in a decrease in entropy
because the adsorbate molecules are restricted in their movement on the surface.
Assertion (A): In physical adsorption, the heat of adsorption is low. Reason (R): Physical adsorption involves weak forces such as van der Waals forces.
Options:
Answer: (1)
Explanation: Physical adsorption involves weak forces such as
van der Waals forces, which result in a low heat of adsorption.
Assertion (A): Catalysis increases the rate of chemical reactions. Reason (R): Catalysts provide an alternative reaction pathway with a lower activation energy.
Options:
Answer: (1)
Explanation: Catalysts provide an alternative pathway with
lower activation energy, thus speeding up the reaction rate.
Assertion (A): Catalysis involves the formation of an intermediate complex between the reactant and the catalyst. Reason (R): The intermediate complex has lower energy, leading to a faster reaction.
Options:
Answer: (1)
Explanation: The formation of an intermediate complex lowers
the activation energy, facilitating a faster reaction.
Assertion (A): The rate of adsorption of a gas on a solid
increases with increasing temperature for chemisorption.
Reason (R): Chemisorption involves the formation of strong
bonds, which is facilitated by higher temperature.
Options:
Answer: (3)
Explanation: Chemisorption typically decreases with an increase
in temperature, as higher temperatures can overcome the bond formation, making
the process less efficient.
Assertion (A): The adsorption of gases on solids is independent
of the surface area of the adsorbent.
Reason (R): More surface area provides more sites for
adsorption, leading to increased adsorption.
Options:
Answer: (4)
Explanation: The adsorption of gases is directly proportional
to the surface area of the adsorbent, meaning the larger the surface area, the
greater the adsorption.
Assertion (A): The adsorption isotherm of gases at low pressure
follows Henry's law.
Reason (R): At low pressure, the gas molecules occupy a small
portion of the surface, resulting in linear adsorption.
Options:
Answer: (1)
Explanation: At low pressure, adsorption follows Henry’s law,
where the amount adsorbed is directly proportional to the pressure.
Assertion (A): Activated charcoal is a good adsorbent for
gases.
Reason (R): Activated charcoal has a high surface area due to
its porous structure, which provides more sites for adsorption.
Options:
Answer: (1)
Explanation: Activated charcoal has a highly porous structure,
which provides a large surface area for adsorption, making it an effective
adsorbent for gases.
Assertion (A): Chemisorption requires a higher activation
energy compared to physisorption.
Reason (R): Chemisorption involves the formation of strong
covalent bonds, whereas physisorption involves weaker forces.
Options:
Answer: (1)
Explanation: Chemisorption requires a higher activation energy
because it involves the formation of strong chemical bonds, which require more
energy compared to the weak interactions in physisorption.
Assertion (A): The adsorption of a gas on a solid is a
spontaneous process.
Reason (R): The enthalpy of adsorption is negative, indicating
that energy is released during the process.
Options:
Answer: (1)
Explanation: Adsorption is an exothermic process, meaning it
releases energy, and hence it is spontaneous.
Assertion (A): The adsorption of gases increases with an
increase in temperature for physical adsorption.
Reason (R): Physical adsorption is endothermic, so increasing
temperature helps in the adsorption process.
Options:
Answer: (4)
Explanation: Physical adsorption decreases with an increase in
temperature, as it is an exothermic process. The correct reasoning would involve
that increasing temperature would reduce the extent of physical adsorption.
Assertion (A): Adsorption is more effective in gases with
larger molecular size.
Reason (R): Larger molecules have more surface area and hence
more opportunity to interact with the adsorbent surface.
Options:
Answer: (1)
Explanation: Larger molecules have more surface area, providing
more adsorption sites, leading to more effective adsorption.
Assertion (A): The heat of adsorption in physical adsorption is
lower than that in chemisorption.
Reason (R): In physical adsorption, the intermolecular forces
are weaker than the chemical bonds formed in chemisorption.
Options:
Answer: (1)
Explanation: The heat of adsorption is lower in physical
adsorption because it involves weak intermolecular forces (like van der Waals
forces), compared to the stronger chemical bonds in chemisorption.
Assertion (A): Adsorption is dependent on the nature of the
adsorbate and adsorbent.
Reason (R): Different adsorbates have different affinities for
different adsorbents, affecting the extent of adsorption.
Options:
Answer: (1)
Explanation: The nature of the adsorbate (its polarity,
molecular size, etc.) and the adsorbent (its surface area, chemical properties)
determine the extent and type of adsorption.
Assertion (A): A decrease in surface area of the adsorbent
decreases the adsorption capacity.
Reason (R): A larger surface area provides more adsorption
sites, thereby increasing the capacity to adsorb molecules.
Options:
Answer: (1)
Explanation: The adsorption capacity of a substance increases
with its surface area because more surface area provides more available sites
for adsorption.
Assertion (A): The process of adsorption involves a decrease in
free energy.
Reason (R): Adsorption is an exothermic process, where energy
is released, leading to a decrease in free energy.
Options:
Answer: (1)
Explanation: Adsorption is an exothermic process, meaning it
releases energy and results in a decrease in free energy.
Assertion (A): Adsorption of gases on solids is always
accompanied by a decrease in entropy.
Reason (R): Adsorption leads to a decrease in randomness as gas
molecules get bound to the solid surface.
Options:
Answer: (1)
Explanation: Adsorption results in the gas molecules being
confined to the surface, which decreases randomness or entropy.
Assertion (A): The adsorption capacity of a solid increases
with increasing pressure at low pressure.
Reason (R): At low pressures, there are more free sites
available on the surface for adsorption.
Options:
Answer: (1)
Explanation: At low pressures, more molecules are available to
interact with the adsorbent surface, leading to an increase in adsorption.
Assertion (A): The rate of adsorption of gases on a solid
increases with an increase in the surface area of the solid.
Reason (R): More surface area provides more adsorption sites
for gas molecules to be adsorbed.
Options:
Answer: (1)
Explanation: An increase in surface area provides more
available sites for adsorption, thereby increasing the rate of adsorption.
Assertion (A): The process of adsorption is reversible in
nature.
Reason (R): Adsorbed molecules can desorb from the surface if
conditions such as temperature or pressure are altered.
Options:
Answer: (1)
Explanation: Adsorption is generally a reversible process, as
increasing temperature or decreasing pressure can cause the adsorbed molecules
to desorb.
Assertion (A): Adsorption and absorption are identical
processes.
Reason (R): Both processes involve the incorporation of
molecules into the bulk of the material.
Options:
Answer: (4)
Explanation: Adsorption involves the accumulation of molecules
on the surface of a material, while absorption involves the incorporation of
molecules into the bulk of the material, so they are distinct processes.
Assertion (A): The process of adsorption follows a Langmuir
isotherm at higher pressures.
Reason (R): At higher pressures, the adsorption sites become
saturated, leading to a plateau in the adsorption curve.
Options:
Answer: (1)
Explanation: The Langmuir adsorption isotherm describes the
saturation of adsorption sites at high pressures, where the rate of adsorption
levels off.
Assertion (A): Physisorption is usually more reversible than
chemisorption.
Reason (R): Physisorption involves weak van der Waals forces,
making it easier for adsorbed molecules to desorb.
Options:
Answer: (1)
Explanation: Physisorption is more reversible because the
forces involved (van der Waals forces) are weak, and hence desorption is easier
compared to chemisorption, which involves stronger chemical bonds.
Assertion (A): Adsorption of gases on solids can lead to an
increase in temperature.
Reason (R): The process of adsorption is exothermic, releasing
heat.
Options:
Answer: (1)
Explanation: Adsorption is an exothermic process, meaning it
releases heat, which can lead to an increase in temperature.
Assertion (A): The rate of chemisorption is typically faster at
lower temperatures.
Reason (R): Chemisorption requires activation energy, which is
more easily achieved at higher temperatures.
Options:
Answer: (4)
Explanation: Chemisorption requires higher temperatures to
overcome the activation energy barrier. Therefore, the rate of chemisorption
generally increases at higher temperatures.
Assertion (A): The effectiveness of an adsorbent can be
measured by its surface area.
Reason (R): A higher surface area provides more available
adsorption sites for adsorbing molecules.
Options:
Answer: (1)
Explanation: A larger surface area provides more sites for
adsorption, making the adsorbent more effective.
Assertion (A): Adsorption is a surface phenomenon.
Reason (R): Adsorption occurs at the surface of a solid, where
the molecules accumulate.
Options:
Answer: (1)
Explanation: Adsorption is a surface phenomenon because it
occurs at the surface of a solid, where the adsorbed molecules are concentrated.
Assertion (A): Chemisorption involves the formation of a
chemical bond between adsorbate and adsorbent.
Reason (R): The strength of chemisorption is greater than that
of physisorption because it involves covalent bonding.
Options:
Answer: (1)
Explanation: Chemisorption involves a chemical bond, such as
covalent bonding, between the adsorbate and adsorbent, making it stronger than
physisorption.
Assertion (A): Physisorption is generally faster than
chemisorption.
Reason (R): Physisorption occurs due to van der Waals forces,
which are weaker and easier to break compared to the stronger chemical bonds
formed in chemisorption.
Options:
Answer: (1)
Explanation: Physisorption involves weaker forces, allowing it
to occur more rapidly compared to chemisorption, which involves stronger
chemical bonds.
Assertion (A): The adsorption isotherm for physisorption
follows the Langmuir adsorption isotherm.
Reason (R): The Langmuir adsorption isotherm assumes a
monolayer adsorption with no interaction between adsorbed molecules.
Options:
Answer: (1)
Explanation: The Langmuir adsorption isotherm is valid for
physisorption as it describes monolayer adsorption with no molecular
interaction, which is characteristic of physisorption.
Assertion (A): In chemisorption, the adsorbed molecules are
bound by covalent bonds.
Reason (R): Covalent bonds are stronger than van der Waals
forces, resulting in chemisorption being stronger and more specific.
Options:
Answer: (1)
Explanation: Chemisorption involves covalent bonds, which are
stronger and more specific than van der Waals forces, leading to stronger and
more selective adsorption.
Assertion (A): The Freundlich adsorption isotherm is applicable
to both physisorption and chemisorption.
Reason (R): The Freundlich isotherm is empirical and accounts
for adsorption that occurs on heterogeneous surfaces.
Options:
Answer: (1)
Explanation: The Freundlich adsorption isotherm applies to both
types of adsorption processes as it describes adsorption on heterogeneous
surfaces, making it suitable for both physisorption and chemisorption.
Assertion (A): Adsorption increases with an increase in
temperature.
Reason (R): An increase in temperature provides more energy for
molecules to adsorb onto the surface.
Options:
Answer: (3)
Explanation: Generally, adsorption decreases with an increase
in temperature for exothermic processes. Adsorption is favored at lower
temperatures, contrary to the assertion.
Assertion (A): Adsorption of gases on solids increases with an
increase in pressure.
Reason (R): At higher pressures, the number of gas molecules
increases, leading to more interactions with the adsorbent.
Options:
Answer: (1)
Explanation: At higher pressures, more gas molecules come into
contact with the surface, leading to an increase in adsorption.
Assertion (A): The formation of a monolayer of adsorbate is a
feature of physisorption.
Reason (R): Physisorption is characterized by weak van der
Waals forces, leading to single-layer adsorption.
Options:
Answer: (1)
Explanation: Physisorption typically forms a monolayer as the
adsorption sites are filled sequentially due to the weak nature of van der Waals
forces.
Assertion (A): Adsorption of gases is usually accompanied by a
decrease in volume.
Reason (R): As gas molecules are adsorbed on the surface, the
free space in the gas phase is reduced.
Options:
Answer: (1)
Explanation: Adsorption reduces the number of free molecules in
the gas phase as they occupy adsorption sites on the surface.
Assertion (A): The adsorption of gases decreases with an
increase in temperature.
Reason (R): Adsorption is an exothermic process, so higher
temperatures provide more energy that can overcome the forces binding the
adsorbed molecules.
Options:
Answer: (1)
Explanation: Adsorption being exothermic is reduced at higher
temperatures because the increase in thermal energy can break the adsorptive
bonds.
Assertion (A): The process of chemisorption is usually
irreversible.
Reason (R): Chemisorption involves the formation of strong
chemical bonds, which are difficult to break.
Options:
Answer: (1)
Explanation: Chemisorption forms strong covalent bonds that are
difficult to reverse, making the process largely irreversible.
Assertion (A): A higher concentration of adsorbate increases
adsorption.
Reason (R): Higher concentration increases the number of
molecules available to interact with the surface of the adsorbent.
Options:
Answer: (1)
Explanation: A higher concentration of the adsorbate leads to
more molecules being available to adsorb on the surface, increasing the amount
of adsorption.
Assertion (A): Adsorption is always an exothermic process.
Reason (R): Adsorption releases energy as bonds are formed
between the adsorbate and adsorbent.
Options:
Answer: (1)
Explanation: Adsorption involves the release of energy as the
adsorbate forms bonds with the adsorbent, making it an exothermic process.
Assertion (A): Activated charcoal is used in gas masks to
adsorb harmful gases.
Reason (R): Activated charcoal has a high surface area that
facilitates the adsorption of gases.
Options:
Answer: (1)
Explanation: Activated charcoal has a very high surface area,
which allows it to adsorb harmful gases effectively, making it ideal for use in
gas masks.
Assertion (A): The process of adsorption is influenced by the
nature of the adsorbent.
Reason (R): Different adsorbents have varying surface areas and
chemical properties that affect their ability to adsorb substances.
Options:
Answer: (1)
Explanation: The adsorption capacity depends on the nature of
the adsorbent, including its surface area and chemical properties, which
determine how effectively it adsorbs different substances.