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

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

Effect of Temperature Change on Reaction Rate

Prawo szybkości reakcji określa zależność między stężeniem reagenta a szybkością reakcji w postaci stałej szybkości "k".
Stała szybkości opisuje zależność między temperaturą a parametrami kinetycznymi odnoszącymi się do zderzenia, orientacji i energii aktywacji reagujących cząsteczek za pomocą równania Arrheniusa. "A" to stała zwana czynnikiem Arrheniusa lub współczynnikiem częstotliwości. "e" jest czynnikiem wykładniczym całkującym energię aktywacji mierzoną w dżulach na mol, stałą gazową i temperaturę w kelwinach.
Zależność temperaturową parametrów można wyjaśnić za pomocą modelu zderzeń, który mówi, że reagujące cząsteczki powinny zderzyć się z wystarczającą energią we właściwej orientacji, aby zainicjować reakcję chemiczną.
Współczynnik częstotliwości składa się z dwóch składowych – częstotliwości zderzeń i współczynnika orientacji. Częstotliwość zderzeń to liczba zderzeń molekularnych w jednostce czasu, podczas gdy współczynnik orientacji opisuje prawdopodobieństwo zderzeń z korzystną orientacją.
Jednak tylko niewielka część zderzeń prowadzi do reakcji. Dzieje się tak, ponieważ reagujące cząsteczki muszą pokonać barierę energetyczną, zwaną energią aktywacji, aby przekształcić się w produkty.
Tylko te cząsteczki, które zderzają się z wystarczającą energią kinetyczną, będą miały wystarczającą energię potencjalną, aby zgiąć, rozciągnąć lub zerwać wiązania, aby przekształcić się w wysokoenergetyczny produkt pośredni zwany stanem przejściowym lub aktywowanym kompleksem. Krótkotrwały, niestabilny aktywowany kompleks traci energię, tworząc stabilne produkty, których całkowita energia jest niższa niż w przypadku reagentów.
Współczynnik wykładniczy w równaniu Arrheniusa reprezentuje ułamek udanych zderzeń, w wyniku których powstają iloczyny. Wzrost temperatury wpływa zarówno na współczynnik częstotliwości, jak i na współczynnik wykładniczy.
W podwyższonych temperaturach cząsteczki poruszają się szybciej, silniej i przy wyższych energiach termicznych, co prowadzi do korzystniejszych zderzeń.
W przypadku większości reakcji wzrost temperatury powoduje wyższą częstotliwość i czynniki wykładnicze, co prowadzi do wzrostu stałej szybkości, co w konsekwencji przekłada się na przyspieszoną szybkość reakcji.

wpływ zmiany temperatury na szybkość reakcji

Równanie Arrheniusa,

wiąże energię aktywacji ze stałą szybkości k dla wielu reakcji chemicznych.

<img alt="Figure1" src="/files/ftp_upload/11698/11698_Equation1.svg" style="text-align: center; height: 30px;">

W tym równaniu R jest stałą gazu doskonałego, która ma wartość 8,314 J/mol·K, T jest temperaturą w stopniach Kelwina, E_a jest energią aktywacji w dżulach na mol, e jest stałą 2,7183, a A jest stałą zwany współczynnikiem częstotliwości, który jest powiązany z częstotliwością zderzeń i orientacją reagujących cząsteczek.

Współczynnik częstotliwości A odzwierciedla, jak dobrze warunki reakcji sprzyjają prawidłowo zorientowanym zderzeniom pomiędzy cząsteczkami reagentów. Zwiększone prawdopodobieństwo efektywnie ukierunkowanych zderzeń skutkuje większymi wartościami A i szybszymi reakcjami.

Wykładniczy składnik e−Eₐ/RT opisuje wpływ energii aktywacji na szybkość reakcji. Zgodnie z teorią kinetyczno-molekularną temperatura materii jest miarą średniej energii kinetycznej tworzących ją atomów lub cząsteczek — niższa energia aktywacji skutkuje większą frakcją cząsteczek o odpowiednim natężeniu energii i szybszą reakcją.

Termin wykładniczy opisuje również wpływ temperatury na szybkość reakcji. Wyższa temperatura oznacza odpowiednio większą część cząsteczek posiadających energię (RT) wystarczającą do pokonania bariery aktywacji (E_a). Daje to wyższą wartość stałej szybkości i odpowiednio większą szybkość reakcji.

Minimalna energia konieczna do utworzenia produktu podczas zderzenia reagentów nazywana jest energią aktywacji (E_a). Różnica w wymaganej energii aktywacji i energii kinetycznej dostarczanej przez zderzające się cząsteczki reagenta jest głównym czynnikiem wpływającym na szybkość reakcji chemicznej. Jeśli energia aktywacji jest znacznie większa niż średnia energia kinetyczna cząsteczek, reakcja będzie przebiegać powoli, ponieważ tylko kilka szybko poruszających się cząsteczek będzie miało wystarczającą energię do reakcji. Jeśli energia aktywacji jest znacznie mniejsza niż średnia energia kinetyczna cząsteczek, duża część cząsteczek będzie miała odpowiednią energię i reakcja będzie przebiegać szybko.

Diagramy reakcji są szeroko stosowane w kinetyce chemicznej w celu zilustrowania różnych właściwości danej reakcji. Pokazuje, jak zmienia się energia układu chemicznego podczas reakcji, w wyniku której reagenty przekształcają się w produkty.

Ten tekst jest adaptacją<a href="https://openstax.org/books/chemistry-2e/pages/12-5-collision-theory">Openstax, Chemistry 2e, Section 12.5: Collision Theory.</a>

Wpływ zmiany temperatury na szybkość reakcji

Równanie Arrheniusa,

Wiąże energię aktywacji i stałą szybkości, k, dla wielu reakcji chemicznych.
W tym równaniu R jest gazem idealnym ...

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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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