Name: reaction order from concentration
Uploaded: 2020-09-24T15:06:50.000Z
Duration: 3 min 3 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.7

IPC.7.F

Concentration and Rate Law

反応の速度は、多くの場合、反応物の濃度に依存します。どのような反応でも、反応速度と反応物濃度の関係は、速度法則または速度方程式を使用して数学的に表すことができます。 
速度の法則では、k は比例定数または速度定数であり、n は単一の反応物に対する反応順序であり、その値は多くの場合整数です。多重反応反応の速度則では、全体的な反応順序はすべての反応順序の合計です。
各反応物について、反応速度、速度定数、濃度、および反応順序はすべて実験的に決定されます。レートの法則は、これらすべてのパラメーター間の関係を表します。 
個々の反応物の順序は、通常、0、1、または2の値を取り、全体的な反応順序に基づいて、化学反応はゼロ次、1次、または2次の反応に分類できます。
単一反応物または単分子化学反応で、反応速度がその持続時間を通じて一定に保たれるものは、ゼロ次反応です。ゼロ次反応における反応物次数はゼロであり、速度の法則によれば、反応物濃度はゼロ乗まで上昇します。
任意の数値を 0 乗に上げると 1 になるため、ゼロ次反応の反応速度は速度定数に等しく、したがって反応物濃度とは無関係です。そのため、ゼロ次反応では、反応物の濃度が下がっても反応速度が遅くなりません。
反応速度が反応物の濃度に正比例する単分子化学反応は、一次反応です。一次反応の反応物次数は 1 であり、速度法則に従って、反応物の濃度は 1 乗に引き上げられます。
1の累乗に乗った任意の数値の値は同じままであるため、1次反応の反応速度は反応物濃度に直接依存します。反応物濃度が減少すると、反応速度は線形に比例して減少します。
反応速度が反応物の濃度の2乗に依存する単分子化学反応は、二次反応です。反応物の次数は2で、反応物の濃度は2乗まで上がります。
したがって、2次反応の反応速度は、反応物濃度の2乗に直接依存します。反応物濃度が減少すると、反応速度は2次関数的に指数関数的に減少します。

濃度と反応速度の関係性

反応速度は、反応物の濃度に影響されます。速度則（微分速度則）または速度式は、化学反応の速度とその反応物の濃度との関係を表す数式です。
 例えば、一般的な反応ではaA + bB ⟶となります。aとbが化学量論係数である場合、反応速度式は次のように記述できます。
   <img alt = "Eq1" src = "/ files / ftp_upload / 11375 / 11375_Equation_1.png" style = "height:50px;" />
 [A]と[B]は反応物のモル濃度を表します。またkは速度定数であり、特定の温度での特定の反応に固有のものです。
 指数mとnは反応次数であり、通常は正の整数ですが、分数、負、またはゼロの値をとる場合もあります。
 速度定数kと反応次数mおよびnは、濃度に応じて反応速度がどのように変化するかを観察することによって実験的に決定されます。速度定数kは反応物の濃度に依存しませんが、上述の通り、温度によって異なります。
 反応速度式の反応次数は、反応物濃度に対する反応速度の数的依存性を表します。次のような一般的な反応速度式について（rate = k [A] m [B] n）、反応はAに関してはmの反応次数を持ち、Bに関してはnの反応次数を持ちます。例えば、m = 1かつn = 2の場合、反応はAで1次、Bで2次です。全体的な反応次数は、単に各反応物の次数の合計です。ここでの反応速度式の例では、反応は全体で3次である（1 + 2 = 3）。
 反応速度式を決定するための一般的な実験的アプローチは、初期反応を用いた方法です。この方法では、さまざまな初期反応物濃度からなる複数の実験における反応速度を測定します。これらの実験で測定された速度を比較することで、反応次数を決定し、続いて速度定数を決定することができます。これらを組み合わせることで、反応速度式を決定できます。
 反応速度式は、一部の反応物について分数の次数を示す場合もあれば、1つの反応物の濃度増加が反応速度低下を引き起こす場合には負の反応次数が観察されることもあります。反応速度式は実験によってのみ決定され、反応式の化学量論によって予測できるわけではないことに注意する必要があります。
 反応次数によって、反応速度と反応物または生成物の濃度との関係が決まります。
 • ゼロ次反応では、反応物の濃度は反応速度に影響を与えず、反応全体にわたって一定に保たれます。 
 • 一次反応では、反応速度は反応物濃度の変化に正比例します。反応物の濃度が低下すると、反応速度も比例して低下します。 
 •  2次以上の反応では、反応速度は反応物の指数値に比例します。したがって、反応が進行して反応物の濃度が低下すると、反応速度は指数関数的に低下します。
 上記の文章は以下から引用しました。 <a href="https://openstax.org/books/chemistry-2e/pages/12-3-rate-laws#57033">Openstax, Chemistry 2e, Section 12.3: Rate Laws</a>.

反応の速度は、反応物の濃度に影響されます。レートの法則(微分レートの法則)またはレート方程式は、数式です...

Education

JoVE Core

Chemistry

化学

Chemical Kinetics

化学反応速度論

KEY TERMS AND CONCEPTS

主要用語と概念

reaction order from concentration

Reaction order from concentration shows how reactant amounts affect reaction rate. Rate laws, also called differential rate laws or rate equations, are mathematical expressions that connect reaction rate with the concentrations of reactants. For a generic reaction a A + b B → products, the rate law can be written using the reactant concentrations [A] and [B] and a rate constant k.

In a rate law, k is the rate constant for one specific reaction at one specific temperature. The exponents m and n are the reaction orders. They are usually positive integers, but they can also be fractions, negative numbers, or zero. The values of k, m, and n are found experimentally by measuring how the rate changes when reactant concentrations change.

The rate constant does not depend on the reactant concentrations, but it can change with temperature. The reaction orders show the mathematical link between concentration and rate. In the expression rate = k [A]m [B]n, the reaction is m order with respect to A and n order with respect to B. For example, if m = 1 and n = 2, the reaction is first order in A and second order in B.

The overall reaction order is the sum of the orders for each reactant. In the example above, the reaction is third order overall because 1 + 2 = 3. A common way to find a rate law is the method of initial rates. In this method, reaction rates are measured in several trials that start with different initial reactant concentrations. Comparing those rates makes it possible to find the reaction orders and then the rate constant.

Rate laws can also include fractional orders. In some cases, a reactant may have a negative order. That means increasing its concentration can lower the reaction rate. Rate laws are determined by experiment only, and they cannot be reliably predicted from reaction stoichiometry. The reaction order also describes how the rate changes as reactant or product concentration changes.

A zero-order reaction has a rate that does not change with reactant concentration. The rate stays constant throughout the reaction. In a first-order reaction, the rate is directly proportional to the change in reactant concentration. As the reactant concentration drops, the rate drops by the same proportion. In second-order or higher-order reactions, the rate depends on the reactants raised to an exponent. As the reaction continues and reactant concentration decreases, the rate falls exponentially.

Reaction Order from Concentration

reaction rate

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concentration and rate law

Reaction order from concentration shows how reactant amounts affect reaction rate. Rate laws, also called differential rate laws or rate equations, are mathematical expressions that connect reaction rate with the concentrations of reactants. For a generic reaction a A + b B → products, the rate law can be written using the reactant concentrations [A] and [B] and a rate constant k. In a rate law, k is the rate constant for one specific reaction at one specific temperature. The exponents m and n...

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Rate laws connect the speed of a chemical reaction to the concentration of its reactants. The rate constant, k, and the reaction orders are not taken from the chemical equation. They are found experimentally by watching how the rate changes when the reactant concentrations change. One common way to do this is the method of initial rates. In this method, several trials are run with different starting concentrations. The measured rates are then compared to determine the reaction orders and,...

the integrated rate law: the dependence of concentration on time

the-integrated-rate-law-the-dependence-of-concentration-on-time

Reading Reaction Progress with Integrated Laws

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half-life of a reaction

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arrhenius plots

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catalysis

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enzymes

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key terms and concepts

Learn how concentration affects reaction rate, how rate laws are written, and how initial rates reveal reaction order, the rate constant, and overall order.

Reaction Order from Concentration | JoVE K12

chemistry

JoVE Core 化学は、簡潔で理解しやすいアニメーションビデオレッスンを使用して、一般的な化学の概念を生き生きとしたものにします。さらに、活動する科学者のビデオでは、現在世界中の実験室で行われている古典的そして独創的な研究・実験をお見せします。

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North Carolina K-12 Science Standard Course of Study

9-12

Matter and its Interactions

PS.Chm.5.1

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Physical Science

Chemical Reactions

3.2.9-12.D

3.2.9-12.E

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Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

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Minnesota Academic Standards in Science

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SC.912.P.12.12

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-5.

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Reaction Order from Concentration

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