Name: arrhenius equation in reaction speed
Uploaded: 2023-04-30T18:28:32.000Z
Duration: 2 min 28 s
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Chemistry

Matter And Its Interactions

HS-PS1-5

effect-of-temperature-change-on-reaction-rate

Effect of Temperature Change on Reaction Rate

La legge della velocità di una reazione definisce la relazione tra la concentrazione di un reagente e la velocità di reazione in termini di una costante di velocità, 'k'.
La costante di velocità descrive la relazione tra la temperatura e i parametri cinetici relativi alla collisione, all'orientamento e all'energia di attivazione delle molecole reagenti tramite l'equazione di Arrhenius. 'A' è una costante chiamata fattore di Arrhenius o fattore di frequenza. 'E' è un fattore esponenziale che integra l'energia di attivazione misurata in joule per mole, la costante del gas e la temperatura in Kelvin.
La dipendenza dalla temperatura dei parametri può essere spiegata con il modello di collisione, che afferma che le molecole reagenti dovrebbero scontrarsi con energia sufficiente nell'orientamento corretto per avviare una reazione chimica.
Il fattore di frequenza è costituito da due componenti: la frequenza di collisione e il fattore di orientamento. La frequenza di collisione è il numero di collisioni molecolari per unità di tempo, mentre il fattore di orientamento descrive la probabilità di collisioni con un orientamento favorevole.
Tuttavia, solo una piccola frazione di collisioni porta a una reazione. Questo perché le molecole reagenti devono superare una barriera energetica, chiamata energia di attivazione, per trasformarsi in prodotti.
Solo quelle molecole che si scontrano con un'energia cinetica sufficiente avranno abbastanza energia potenziale per piegare, allungare o rompere i legami per trasformarsi in un intermedio ad alta energia chiamato stato di transizione, o complesso attivato. Il complesso attivato instabile e di breve durata perde energia per formare prodotti stabili, la cui energia totale è inferiore a quella dei reagenti.
Il fattore esponenziale nell'equazione di Arrhenius rappresenta la frazione di collisioni riuscite che hanno portato a prodotti. Un aumento della temperatura influenza sia il fattore di frequenza che il fattore esponenziale.
A temperature elevate, le molecole si muovono più velocemente, con più forza e con energie termiche più elevate, portando a collisioni più favorevoli.
Per la maggior parte delle reazioni, un aumento della temperatura si traduce in fattori esponenziali e di frequenza più elevati, portando ad un aumento della costante di velocità, che si traduce di conseguenza in una velocità di reazione accelerata.

effetto del cambiamento della temperatura sulla velocità di reazione

L'equazione di Arrhenius,

<img alt="Figure1" src="/files/ftp_upload/11698/11698_Equation1.svg" style="text-align: center; height: 30px;">

mette in relazione l'energia di attivazione e la costante di velocità, k, per molte reazioni chimiche.

In questa equazione, R è la costante dei gas ideali, che ha un valore 8,314 J/mol·K; T è la temperatura in Kelvin; E_a è l'energia di attivazione in Joule per mole; e è la costante 2,7183; e A è una costante chiamata fattore di frequenza, correlato alla frequenza delle collisioni e all'orientamento delle molecole reagenti.

Il fattore di frequenza, A, riflette quanto bene le condizioni di reazione favoriscano le collisioni correttamente orientate tra le molecole dei reagenti. Una maggiore probabilità di collisioni effettivamente orientate si traduce in valori più grandi di A e velocità di reazione più rapide.

Il termine esponenziale, e−Eₐ/RT, descrive l'effetto dell'energia di attivazione sulla velocità di reazione. Secondo la teoria cinetica molecolare, la temperatura della materia è una misura dell’energia cinetica media dei suoi atomi o molecole costituenti: un’energia di attivazione inferiore si traduce in una frazione più significativa di molecole adeguatamente energizzate e in una reazione più rapida.

Il termine esponenziale descrive anche l'effetto della temperatura sulla velocità di reazione. Una temperatura più elevata rappresenta una frazione corrispondentemente maggiore di molecole che possiedono energia sufficiente (RT) per superare la barriera di attivazione (E_a). Ciò produce un valore più elevato per la costante di velocità e una velocità di reazione corrispondentemente più rapida.

L'energia minima necessaria per formare un prodotto durante una collisione tra reagenti è chiamata energia di attivazione (E_a). La differenza nell'energia di attivazione richiesta e nell'energia cinetica fornita dalle molecole dei reagenti in collisione è un fattore primario che influenza la velocità di una reazione chimica. Se l’energia di attivazione è molto maggiore dell’energia cinetica media delle molecole, la reazione avverrà lentamente, poiché solo poche molecole che si muovono velocemente avranno abbastanza energia per reagire. Se l'energia di attivazione è molto inferiore all'energia cinetica media delle molecole, una grande frazione di molecole sarà adeguatamente energetica e la reazione procederà rapidamente.

I diagrammi di reazione sono ampiamente utilizzati nella cinetica chimica per illustrare varie proprietà di una reazione di interesse. Essi mostrano come cambia l'energia di un sistema chimico mentre subisce una reazione, convertendo i reagenti in prodotti.

Questo testo è adattato da <a href="https://openstax.org/books/chemistry-2e/pages/12-5-collision-theory">Openstax, Chemistry 2e, Section 12.5: Collision Theory.</a>

Effetto del cambiamento della temperatura sulla velocità di reazione

L'equazione di Arrhenius,

Mette in relazione l'energia di attivazione e la costante di velocità, k, per molte reazioni chimiche.
In questa equazione, R è il gas ideale ...

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arrhenius equation in reaction speed

The Arrhenius equation connects activation energy, temperature, and the rate constant, k, for many chemical reactions. It helps explain why some reactions move slowly while others happen faster.

In this equation, R is the ideal gas constant, with a value of 8.314 J/mol·K. T is the temperature in kelvin, Ea is the activation energy in joules per mole, e is the constant 2.7183, and A is the frequency factor.

The frequency factor, A, describes how often reacting molecules collide and how well they are oriented during those collisions. Better orientation increases the chance of effective collisions. That leads to larger A values and faster reaction rates.

The exponential term, e−Ea/RT, shows how activation energy affects the reaction rate. Kinetic molecular theory says that temperature measures the average kinetic energy of atoms or molecules. When activation energy is lower, more molecules have enough energy to react, and the reaction is faster.

The same exponential term also shows the effect of temperature. At higher temperature, a larger fraction of molecules has enough energy, RT, to get over the activation barrier, Ea. This increases the rate constant and speeds up the reaction.

Activation energy is the minimum energy needed to form products during a collision between reactants. If Ea is much larger than the average kinetic energy of the molecules, only a few fast-moving molecules can react, so the reaction is slow. If Ea is much smaller than the average kinetic energy, many molecules can react, so the reaction proceeds quickly.

Reaction diagrams are often used in chemical kinetics to show how a system’s energy changes as reactants turn into products. They help visualize the energy barrier and the path from reactants to products. This text is adapted from Openstax, Chemistry 2e, Section 12.5: Collision Theory.

Arrhenius Equation in Reaction Speed

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effect of temperature change on reaction rate

The Arrhenius equation connects activation energy, temperature, and the rate constant, k, for many chemical reactions. It helps explain why some reactions move slowly while others happen faster. In this equation, R is the ideal gas constant, with a value of 8.314 J/mol·K. T is the temperature in kelvin, Ea is the activation energy in joules per mole, e is the constant 2.7183, and A is the frequency factor. The frequency factor, A, describes how often reacting molecules collide and how well...

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Explore how the Arrhenius equation links temperature, activation energy, and collision orientation to reaction speed in high school chemistry.

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Arrhenius Equation in Reaction Speed

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