Exam (elaborations)
XII_Chem_New_Chap-03 Chemical Kinetics (91 AR Items)
XII_Chem_New_Chap-03 Chemical Kinetics (91 AR Items)
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Spread the Happiness. Assertion and Reason Statements Feedback: 9008271516XII_CHEMISTRY_NEW_CHAPTER-03: CHEMICAL KINETICS _ A&R TEST ITEMS
# Correct Assertion Correct Reason
3.1 Rate of a Chemical Reaction
Chemical kinetics studies reaction rates, not just It delves beyond thermodynamics' "can it happen" to explore the "how
1
feasibility. fast" of reactions.
Rate of a reaction quantifies concentration change This captures the essence of reaction speed, reflecting how quickly
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per unit time. reactants convert to products.
Average rate provides a general idea of reaction It considers the overall concentration change, offering a broad picture
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speed within a timeframe. but not necessarily the exact rate at any moment.
Instantaneous rate pinpoints the reaction speed at It represents the most precise measure of reaction speed at a single
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a specific moment. point in time.
The slope of the tangent line to the concentration- This graphical approach translates the curve's steepness into a
5 time curve reflects instantaneous rate. numerical value, signifying the rate of change at that instant.
Stoichiometric coefficients account for unequal They ensure the rate reflects the contribution of each species based on
6 reactant/product involvement in rate expressions. their participation ratios in the reaction.
Gaseous reaction rates can be expressed in terms Since partial pressure directly relates to concentration at constant
7 of partial pressure change. temperature, it offers an equivalent way to represent reaction speed.
3.2 Factors Influencing Rate of a Reaction
Concentration and temperature affect reaction Collisions between reactant molecules are more frequent and forceful
8 rate. at higher concentrations and temperatures, leading to faster reactions.
Rate law is a mathematical equation. It describes the quantitative relationship between reaction rate and
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reactant concentrations.
Order of reaction reflects sensitivity to It's an experimental value determined from the rate law expression.
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concentration changes.
Zero and first-order reactions have simpler Their rate laws involve exponents of 0 or 1 for reactant concentrations.
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relationships with concentration.
Second-order reactions exhibit a quadratic or Their rate laws involve exponents of 2 for one reactant or 1 each for
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multiplicative dependence on concentration. two reactants.
Catalyst accelerates reactions by lowering the It provides an alternative reaction pathway with a lower energy barrier
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activation energy. for successful collisions.
Molecularity refers to the number of reactants in a It defines the specific collision requirement for the fundamental
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single reaction step. reaction mechanism.
Order is an experimental observation, while Order reflects the overall rate dependence, while molecularity
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molecularity is inherent to the mechanism. describes the specific collision dynamics in a single step.
The rate-determining step dictates the overall rate The slowest step limits the pace at which subsequent steps can occur.
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in complex reactions.
Rate law expresses reaction rate in terms of It offers a quantitative measure of how concentration changes affect
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concentration. the reaction speed.
Exponents in a rate law quantify the influence of They indicate the degree to which the reaction rate depends on each
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concentration changes. reactant's concentration.
Order is determined by experiments, not the The balanced equation reflects overall stoichiometry, while
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balanced equation. experiments reveal the actual rate dependence on concentration.
The sum of exponents provides the overall It combines the individual effects of each reactant on the collective
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reaction order. reaction rate.
Molecularity is only applicable to elementary The concept of simultaneous collision is relevant only for fundamental
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reactions. one-step reactions.
Order applies to all reactions, while molecularity is Order reflects the experimental dependence on concentration,
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limited to elementary ones. regardless of the mechanism.
In complex reactions, the order is determined by The slowest step dictates the overall rate, and its molecularity reflects
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the rate-determining step's molecularity. the number of species involved in the critical step.
Increasing concentration in a second-order The rate is directly proportional to the concentration raised to the
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reaction leads to a squared rate increase. power of the order (2 in this case).
3.3 Integrated Rate Equations
Integrated rate equations relate measured They express the change in concentration ([R]) over time (t) based on
25 concentration-time data to the rate constant (k). reaction order (zero or first).
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XII_CHEMISTRY_NEW_CHAPTER-03: CHEMICAL KINETICS _ A&R TEST ITEMS
# Correct Assertion Correct Reason
Integrated rate equations enable prediction of Knowing the rate constant (k) and initial concentration ([R]0) allows
26
concentration changes in a reaction. calculating concentration at any future time (t).
Integration of the differential rate equation Integrating accounts for the continuous change in concentration over
27 explains the concentration-time relationship in a time, unlike the instantaneous rate in the differential rate equation.
specific reaction order.
Zero-order integrated rate equations show a direct A higher initial concentration ([R]₀) in a zero-order reaction leads to a
28 proportionality between initial concentration longer half-life (t₁/₂) due to more reactant to deplete.
([R]₀) and half-life (t₁/₂).
First-order integrated rate equations confirm the The rate in first-order reactions depends only on the rate constant (k),
29 independence of half-life (t₁/₂) from initial making t₁/₂ independent of [R]₀.
concentration ([R]₀).
Integrated rate equations provide a tool to The time for near-completion is approximately ten times the half-life
30 estimate the time required for near-completion (t₁/₂), highlighting a practical application.
(99.9%) in first-order reactions.
Zero-order reactions are characterized by a rate This inherent property implies a constant change in concentration over
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independent of reactant concentration. time.
The zero-order integrated rate equation expresses The equation is [R] = -kt + [R]₀, where the slope is -k and the intercept is
32 a linear relationship between concentration ([R]) [R]₀.
and time (t).
The zero-order rate constant (k) is inversely A smaller rate constant (k) leads to a slower decrease in concentration,
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proportional to the half-life (t₁/₂). resulting in a longer half-life.
First-order reactions are defined by a rate This proportionality signifies that the reaction rate is directly
34 proportional to the first power of the reactant dependent on the concentration of the reactant.
concentration.
The first-order integrated rate equation expresses The equation is ln[R] = -kt + ln[R]₀, where the slope is -k and the
35 a relationship between the natural logarithm of intercept is ln[R]₀.
concentration (ln[R]) and time (t).
The first-order rate constant (k) determines the A higher rate constant (k) leads to a faster decrease in concentration,
36 rate of disappearance of the reactant and resulting in a shorter half-life.
influences its half-life (t₁/₂).
3.4 Temperature Dependence of the Rate of a Reaction
Temperature dependence: Higher T, more Increased kinetic energy at higher temperatures leads to more
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frequent collisions with activation energy. successful collisions.
Rate constant near doubling with 10°C increase: Consistent with the exponential term (e^-Ea/RT) in the equation.
38 Reflects Arrhenius equation's exponential
dependence.
Pseudo first-order reactions: Mimic first-order Constant concentration of the excess reactant simplifies the rate law.
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kinetics due to one reactant's excess.
Activation energy and reaction rate: Higher Ea Fewer molecules possess the energy to overcome the higher energy
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leads to slower reaction rate. barrier.
Arrhenius equation analysis: ln(k) vs. 1/T yields a Enables calculation of activation energy (Ea) and pre-exponential factor
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straight line (slope & intercept). (A) from the graph.
Catalyst action: Lowers potential energy barrier, Provides an alternate pathway with lower activation energy, facilitating
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accelerating the reaction. faster product formation.
Catalyst characteristics: Increases reaction rate Catalyst participates in the reaction but remains unchanged at the end.
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without permanent chemical change.
Catalyst effect and equilibrium: Catalyst does not It only accelerates both forward and reverse reactions to reach
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alter the equilibrium constant. equilibrium faster.
3.5 Collision Theory of Chemical Reactions
Effective collision: Prerequisite for reaction; Successful collisions involve overcoming the energy barrier and
45 requires sufficient energy and proper orientation. achieving optimal alignment for bond-breaking and formation.
Steric factor (P): Accounts for probability of Considers the influence of molecular shape and functional groups on
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effective collisions. the likelihood of a reaction occurring.
Collision theory limitations: Considers Ignores factors like electron distribution and intermolecular forces,
47 atoms/molecules as hard spheres, neglecting potentially impacting collision dynamics.
structural details.
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