What traumatic event does Zitkala-Sa describe at the school?

The forcible cutting of her long hair

Why was the cutting of her hair so humiliating to Zitkala-Sa?

Among her people, shingled hair was worn by cowards and mourners

Distinguish between average and instantaneous rate.

Average rate is the change over a finite interval; instantaneous rate is the rate at a particular instant, the limit as the interval tends to zero.

What is the difference between order and molecularity?

Order is experimental and can be fractional or zero, while molecularity is a theoretical whole number for an elementary step.

Why is the half-life of a first order reaction independent of concentration?

Because \(t_{1/2}=\dfrac{0.693}{k}\), which contains only the rate constant.

What are the units of the rate constant for a first order reaction?

Time\(^{-1}\) (for example s\(^{-1}\)), independent of concentration.

How does temperature affect the rate constant?

A rise in temperature increases \(k\); roughly the rate doubles for every 10 K rise.

State the Arrhenius equation and define its terms.

\(k=Ae^{-E_a/RT}\), where \(A\) is the frequency factor, \(E_a\) the activation energy and \(T\) the temperature.

What two conditions must colliding molecules satisfy to react?

They must collide with energy equal to or greater than the activation energy and with the correct orientation.

How does a catalyst increase reaction rate?

It provides an alternative path with a lower activation energy, without itself being consumed.

What is the threshold energy of a reaction?

The minimum total energy that colliding molecules must possess for an effective (reactive) collision.

CBSE · Senior secondary

CBSE Class 12 — Notes, Chapters & Practice Quizzes

Q: Write the integrated rate equation for a first order reaction.

\(k=\dfrac{2.303}{t}\log\dfrac{[A]_0}{[A]}\).

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Chapter 3: Chemical Kinetics — Class 12 Chemistry

Chemistry · 10 chapters

Summary, key terms, important questions and a practice quiz with AI diagnosis for each.

Chapter 3: Chemical Kinetics

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The rate of a chemical reaction is defined as:

Summary

Chemical kinetics deals with the rates of reactions, the factors that control them and the mechanisms by which they occur. The rate of a reaction is the change in concentration of a reactant or product per unit time, expressed as average or instantaneous rate. The rate depends on concentration through the rate law, \(\text{rate}=k[A]^x[B]^y\), where the exponents give the order with respect to each reactant and their sum is the overall order; \(k\) is the rate constant. Order is determined experimentally and may differ from the stoichiometric coefficients, while molecularity refers to the number of species in an elementary step. Integrated rate equations give concentration as a function of time: zero order reactions have rate independent of concentration, and first order reactions follow \(k=\dfrac{2.303}{t}\log\dfrac{[A]_0}{[A]}\) with a constant half-life. Temperature strongly affects rate; the Arrhenius equation \(k=Ae^{-E_a/RT}\) links the rate constant to the activation energy \(E_a\) and temperature. According to collision theory, only molecules colliding with sufficient energy and proper orientation react, and a catalyst speeds up a reaction by providing an alternative path of lower activation energy without being consumed.

Rate of reaction and rate lawOrder and molecularityIntegrated rate equations (zero and first order)Half-life of reactionsTemperature dependence and Arrhenius equationCollision theory and catalysis

Key terms

Rate of reaction

The change in concentration of a reactant or product per unit time.

Rate law

An experimentally determined equation expressing rate in terms of concentrations, \(\text{rate}=k[A]^x[B]^y\).

Order of reaction

The sum of the powers of the concentration terms in the rate law.

Molecularity

The number of reacting species taking part in an elementary reaction step.

Activation energy

The minimum extra energy \(E_a\) reactant molecules must possess to react.

Arrhenius equation

Relates rate constant to temperature, \(k=Ae^{-E_a/RT}\).

Important questions

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The change in concentration of a reactant or product per unit time.

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Practice quiz · Chemical Kinetics

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Chemical Kinetics

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