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

反応の速度法則は、反応物濃度と反応速度との関係を速度定数「k」で定義します。
速度定数は、アレニウス方程式を介して、反応する分子の衝突、配向、および活性化エネルギーに関連する温度と運動パラメータとの関係を表します。「A」は、アレニウス因子または周波数係数と呼ばれる定数です。「e」は、ジュール/モルで測定された活性化エネルギー、ガス定数、およびケルビン単位の温度を統合した指数関数的因子です。
パラメータの温度依存性は、反応する分子が正しい向きで十分なエネルギーと衝突して化学反応を開始する必要があるという衝突モデルで説明できます。
周波数係数は、衝突周波数と方向係数の 2 つのコンポーネントを構成します。衝突頻度は単位時間あたりの分子衝突の数であり、配向係数は好ましい配向との衝突の確率を表します。
それでも、衝突のごく一部だけが反応につながります。これは、反応する分子が製品に変換するために、活性化エネルギーと呼ばれるエネルギー障壁を克服しなければならないためです。
十分な運動エネルギーと衝突する分子だけが、結合を曲げたり、伸ばしたり、切断したりするのに十分な位置エネルギーを持ち、遷移状態または活性化複合体と呼ばれる高エネルギーの中間体に変化します。短寿命で不安定な活性化錯体は、エネルギーを失い、安定した生成物を形成し、その総エネルギーは反応物よりも低くなります。
アレニウス方程式の指数係数は、成功した衝突のうち、製品が得られる割合を表します。温度の上昇は、周波数係数と指数係数の両方に影響します。
高温では、分子はより速く、より力強く、より高い熱エネルギーで移動するため、より有利な衝突につながります。
ほとんどの反応では、温度が上昇すると、周波数と指数関数的な要因が高くなり、速度定数が上昇し、その結果、反応速度が加速されます。

反応速度に対する温度変化の影響

アレニウス方程式は、多くの化学反応の活性化エネルギーと速度定数 k に関連します。



<img alt="Figure1" src="/files/ftp_upload/11698/11698_Equation1.svg" style="text-align: center; height: 30px;">



この式では、R は理想気体定数であり、その値は 8.314 J/mol・K、T は温度 (ケルビン)、E_a は活性化エネルギー (ジュール/モル)、e は定数 2.7183、A は定数になります。 これは周波数係数と呼ばれ、衝突の頻度と反応する分子の方向に関連しています。

周波数係数 A は、反応条件が反応物分子間の正しい方向の衝突にどの程度適しているかを反映します。 効果的に方向付けられた衝突の確率が増加すると、A の値が大きくなり、反応速度が速くなります。

指数項 e−Eₐ/RT は、反応速度に対する活性化エネルギーの影響を表します。 運動分子理論によれば、物質の温度は、その構成原子または分子の平均運動エネルギーの尺度です。活性化エネルギーが低いほど、適切にエネルギーを与えられた分子の割合がより多くなり、反応が速くなります。

指数項は、反応速度に対する温度の影響も表します。 温度が高いほど、活性化障壁 (E_a) を克服するのに十分なエネルギー (RT) を有する分子の割合がそれに応じて多くなります。 これにより、速度定数の値が大きくなり、それに応じて反応速度も速くなります。

反応物間の衝突中に生成物を形成するために必要な最小エネルギーは、活性化エネルギー (E_a) と呼ばれます。 必要な活性化エネルギーと、衝突する反応物分子によって提供される運動エネルギーの差は、化学反応の速度に影響を与える主な要因です。 活性化エネルギーが分子の平均運動エネルギーよりもはるかに大きい場合、反応に十分なエネルギーを持つのは高速で移動する少数の分子だけであるため、反応はゆっくりと起こります。 活性化エネルギーが分子の平均運動エネルギーよりもはるかに小さい場合、分子の大部分は十分なエネルギーを持ち、反応は急速に進行します。

反応図は、対象の反応のさまざまな特性を示すために化学反応速度論で広く使用されています。 これは、化学システムが反応を起こし、反応物が生成物に変換されるにつれてエネルギーがどのように変化するかを示します。

このテキストはから翻案されます <a href="https://openstax.org/books/chemistry-2e/pages/12-5-collision-theory">Openstax, Chemistry 2e, Section 12.5: Collision Theory.</a>

アレニウス方程式、

多くの化学反応の活性化エネルギーと速度定数Kを関連付けます。
この方程式では、Rは理想気体です...

Education

JoVE Core

Organic Chemistry

有機化学

Unit 1

ユニット1

Thermodynamics and Chemical Kinetics

熱力学と化学反応速度論

KEY TERMS AND CONCEPTS

主要用語と概念

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...

enthalpy and heat of reaction

Combustion Heat and Hydrocarbon Stability

Combustion is a burning reaction that releases energy as heat, light, or sound. It happens when a substance reacts with an oxidizing agent, usually molecular oxygen. The heat of combustion is also called the enthalpy of combustion. The energy released when one mole of a substance undergoes complete combustion at constant pressure is the molar heat of combustion. Combustion reactions are exothermic, so they give off energy. For that reason, the sign of ΔH is negative. In 1772, Antoine Lavoisier...

energetics of solution formation

Why Some Solutions Form Spontaneously

Solution formation can happen spontaneously under the right conditions. A spontaneous process is one that occurs without energy from an outside source. During dissolution, solute and solvent particles separate and then attract each other in a new way. The energy change depends on the balance of intermolecular forces, which are the attractions between particles. If the solute-solute and solvent-solvent forces are about the same as the new solute-solvent forces, the solution forms with no energy...

entropy and solvation

Hydrophobic Effects in Solvation

Solvation is the process of surrounding a solute with solvent. It spreads the solute evenly through the solvent. A useful rule is that like dissolves like. A good solvent has molecular features similar to the substance being dissolved. Polar solvents dissolve polar solutes, and apolar solvents dissolve apolar solutes. A polar solvent has a high dielectric constant, with ε greater than or equal to 15. An apolar solvent has a low dielectric constant. The dielectric constant is defined by the...

gibbs free energy and thermodynamic favorability

gibbs-free-energy-and-thermodynamic-favorability

Temperature Effects on Gibbs Free Energy

Temperature changes can decide whether a process is spontaneous. This idea applies to phase changes and to some chemical reactions. The key link is Gibbs free energy, which connects free energy change with enthalpy and entropy. The sign of the Gibbs free energy change, or ΔG, depends on the signs of enthalpy change (ΔH) and entropy change (ΔS), and sometimes on the absolute temperature. Because temperature is measured in kelvin, it is always a positive value. That means there are four main...

chemical and solubility equilibria

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Solubility depends on free energy changes when a solute dissolves in a solvent. The free energy change for this process is called the free energy of solution, ΔGsolution. When ΔGsolution is less than zero, solution formation is favorable. When it is greater than zero, solution formation is unfavorable. For complete dissolution to happen, the Gibbs energy change must be negative. This means the balance of forces in the mixture must favor solution formation. The amount a solute dissolves in a...

rate law and reaction order

How Reactant Concentration Sets Reaction Rate

Reaction rate depends on reactant concentration, and rate laws show that relationship with a mathematical equation. A rate law, also called a differential rate law or rate equation, links the rate of a chemical reaction to the concentrations of its reactants. For a generic reaction, a A + b B  products, the rate law can be written as rate = k [A]^m [B]^n. Here, [A] and [B] are the molar concentrations of the reactants. The constant k is the rate constant, and it is specific to one reaction at...

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

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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

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predicting reaction outcomes

How Temperature Changes Reaction Rate

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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 有機化学では、立体化学、反応、メカニズムの基本概念を、簡潔でわかりやすいアニメーション ビデオ レッスンを使用して説明します。さらに、科学者の実際のビデオでは、世界中の今日の研究室で行われている古典的および独自の研究実験における関連概念の適用を示しています。

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

The Periodic Table

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Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level and the composition of the nucleus of atoms.  Clarification Statement: Chemistry: Examples of properties that could be predicted from patterns could include reactivity of metals, types of bonds formed, numbers of bonds formed, atomic radius, atomic mass, or reactions with oxygen. Emphasis is on main group elements and qualitative understanding of the relative trends of ionization energy and electronegativity.

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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