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

K12 Standards

Louisiana Student Standards for Science

High School

Chemistry

Matter And Its Interactions

HS-PS1-5

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

Effect of Temperature Change on Reaction Rate

Закон скорости реакции определяет отношение между концентрацией реагента и скоростью реакции в терминах константы скорости «k».
Константа скорости описывает соотношение между температурой и кинетическими параметрами, относящимися к столкновению, ориентации и энергии активации реагирующих молекул с помощью уравнения Аррениуса. «A» — это константа, называемая фактором Аррениуса или коэффициентом частоты. «e» — экспоненциальный фактор, интегрирующий энергию активации, измеряемую в джоулях на моль, газовую постоянную и температуру в кельвинах.
Температурную зависимость параметров можно объяснить с помощью модели столкновения, которая гласит, что реагирующие молекулы должны сталкиваться с достаточной энергией в правильной ориентации, чтобы инициировать химическую реакцию.
Коэффициент частоты состоит из двух составляющих — частоты столкновений и коэффициента ориентации. Частота столкновений — это количество молекулярных столкновений в единицу времени, тогда как коэффициент ориентации описывает вероятность столкновений с благоприятной ориентацией.
Тем не менее, лишь небольшая доля столкновений приводит к реакции. Это связано с тем, что реагирующие молекулы должны преодолеть энергетический барьер, называемый энергией активации, чтобы превратиться в продукты.
Только те молекулы, которые сталкиваются с достаточной кинетической энергией, будут обладать достаточной потенциальной энергией, чтобы изгибаться, растягиваться или разрывать связи и превращаться в высокоэнергетический промежуточный продукт, называемый переходным состоянием, или активированным комплексом. Короткоживущий, нестабильный активированный комплекс теряет энергию для образования стабильных продуктов, суммарная энергия которых ниже, чем у реагентов.
Экспоненциальный множитель в уравнении Аррениуса представляет собой долю успешных столкновений, приводящих к образованию продуктов. Повышение температуры влияет как на частотный фактор, так и на экспоненциальный фактор.
При повышенных температурах молекулы движутся быстрее, сильнее и с более высокими тепловыми энергиями, что приводит к более благоприятным столкновениям.
Для большинства реакций повышение температуры приводит к увеличению частоты и экспоненциальных коэффициентов, что приводит к увеличению константы скорости и, следовательно, к ускорению скорости реакции.

Влияние изменения температуры на скорость реакции

Уравнение Аррениуса,

связывает энергию активации и константу скорости k для многих химических реакций.

<img alt="Figure1" src="/files/ftp_upload/11698/11698_Equation1.svg" style="text-align: center; height: 30px;">

В этом уравнении R — постоянная идеального газа, имеющая значение 8,314 Дж/моль·К, T — температура в кельвинах, E_a — энергия активации в джоулях на моль, e — константа, равная 2,7183, а A - это постоянная, называемая частотным фактором, которая связана с частотой столкновений и ориентацией реагирующих молекул.

Частотный фактор A отражает, насколько хорошо условия реакции благоприятствуют правильно ориентированным столкновениям между молекулами реагентов. Повышенная вероятность эффективно ориентированных столкновений приводит к увеличению значений A и более высокой скорости реакции.

Экспоненциальный член e−Eₐ/RT описывает влияние энергии активации на скорость реакции. Согласно кинетической молекулярной теории, температура вещества является мерой средней кинетической энергии составляющих его атомов или молекул: более низкая энергия активации приводит к более значительной доле молекул с адекватной энергией и более быстрой реакции.

Экспоненциальный член также описывает влияние температуры на скорость реакции. Более высокая температура представляет собой соответственно большую долю молекул, обладающих достаточной энергией (RT) для преодоления активационного барьера (E_a). Это дает более высокое значение константы скорости и, соответственно, более высокую скорость реакции.

Минимальная энергия, необходимая для образования продукта при столкновении реагентов, называется энергией активации (Е_а). Разница в требуемой энергии активации и кинетической энергии, обеспечиваемой сталкивающимися молекулами реагентов, является основным фактором, влияющим на скорость химической реакции. Если энергия активации намного больше средней кинетической энергии молекул, реакция будет происходить медленно, так как лишь немногим быстро движущимся молекулам будет достаточно энергии для реакции. Если энергия активации намного меньше средней кинетической энергии молекул, большая часть молекул будет обладать достаточной энергией, и реакция будет протекать быстро.

Диаграммы реакций широко используются в химической кинетике для иллюстрации различных свойств интересующей реакции. Он показывает, как меняется энергия химической системы в ходе реакции, превращающей реагенты в продукты.

Уравнение Аррениуса,

Связывает энергию активации и константу скорости K для многих химических реакций.
В этом уравнении R является идеальным газом ...

Education

JoVE Core

Organic Chemistry

Органическая химия

Unit 1

Раздел 1

Thermodynamics and Chemical Kinetics

Термодинамика и химическая кинетика

KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

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

chemical reactions

Stoichiometry, Rates, and Equilibrium

Stoichiometry, reaction rates, and equilibrium explain how chemical reactions are measured and predicted. A balanced chemical equation shows the chemical formulas of the reactants and products in a chemical change. It also gives the relative amounts of each substance involved. Reaction stoichiometry helps predict how much reactant is needed to make a desired amount of product. It can also show how much product forms from a given amount of reactant. The amounts shown by a balanced equation are...

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energetics of solution formation

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entropy and solvation

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gibbs free energy and thermodynamic favorability

gibbs-free-energy-and-thermodynamic-favorability

Temperature Effects on Gibbs Free Energy

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rate law and reaction order

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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...

multi-step reactions

Reaction Mechanisms and Rate-Determining Steps

Chemical reactions can happen in a sequence of steps. A balanced chemical equation shows the reactants and products, but it does not show how the reaction occurs at the molecular level. The reaction mechanism, or reaction path, gives that step-by-step detail. Each step in a mechanism is an elementary reaction. These elementary reactions happen in order, and together they add up to the balanced equation for the overall reaction. In a multistep mechanism, one step is often much slower than the...

bond dissociation energy and activation energy

bond-dissociation-energy-and-activation-energy

How Bond Strength Shapes Reaction Speed

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energy diagrams, transition states, and intermediates

energy-diagrams-transition-states-and-intermediates

Reaction Coordinate Diagrams in Chemical Reactions

Reaction coordinate diagrams show how energy changes during a chemical reaction. These free-energy graphs use the horizontal axis to show reaction progress. Points near the reactants look like the reactants, while points near the products look like the products. The peaks on the diagram represent stable structures with measurable lifetimes. Other points on the curve are unstable and cannot be isolated. The high-energy, unstable peak is called the transition state, or activated complex. At the...

predicting reaction outcomes

How Temperature Changes Reaction Rate

Reaction rate and reaction pathway are key ideas in chemical kinetics. Thermodynamics, by contrast, focuses on the state of a system. It describes the properties, behavior, and components of reactants and products. It does not describe the path of the process or the speed of the reaction. Kinetics gives information on the atomic or molecular level, while thermodynamics focuses on the energetics of the reactants and products. Thermodynamics can show what may happen in a reaction, but it does...

key terms and concepts

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

Arrhenius Equation in Reaction Speed | JoVE K12

organic chemistry

JoVE Core Organic Chemistry explains basic concepts of stereochemistry, reactions, and mechanisms using concise and easy-to-understand animated video lessons. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Minnesota Academic Standards in Science

9-12

3.2.1 9C.3.1.1.2

Florida Department of Education

Physical Science

SC.912.P.12

SC.912.P.12.12

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HS-PS1-1

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HS-PS1-3

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HS-PS1-4

The Arrhenius equation,

relates the activation energy and the rate constant, k, for many chemical reactions.
In this equation, R is the ideal gas ...

Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.  Clarification Statement: Student reasoning should focus on the number and energy of collisions between molecules.  Emphasis is on simple reactions in which there are only two reactants; evidence from temperature, concentration, and rate data;  and qualitative relationships between rate and temperature.

Arrhenius Equation in Reaction Speed

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