Name: how reactant concentration sets reaction rate
Uploaded: 2025-05-22T09:05:33.000Z
Duration: 2 min 33 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Physical Science

SC.912.P.12

SC.912.P.12.12

Rate Law and Reaction Order

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。 
レート法則では、「k」は比例定数またはレート定数であり、「n」は単一の反応物に対する反応順序であり、その値はしばしば整数です。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。
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。ゼロ次反応の反応物次数はゼロであり、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。
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。1 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 乗に上昇します。
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。

レートの法則と反応順序

反応速度は反応物の濃度によって影響を受けます。 速度法則 (微分速度則) または速度方程式は、化学反応の速度とその反応物質の濃度の間の関係を説明する数式です。

たとえば、一般的な反応 aA + bB ⟶ 生成物 (a と b は化学量論係数) では、速度の法則は次のように記述できます。

レート = k[A]^m[B]^n

[A] と [B] は反応物のモル濃度を表し、k は速度定数であり、特定の温度において、その反応に固有の値です。

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、負の値、またはゼロの場合もあります。

速度定数 k と反応次数 m および n は、反応物の濃度が変化すると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証明されます。 速度定数 k は反応物質の濃度には依存しませんが、温度によって変化します。

速度則における反応順序は、反応物質の濃度に対する速度の数学的依存性を表します。 一般的な速度法則 (rate = k[A]^m[B]^n) を参照すると、反応は A に関しては m、B に関しては nとなります。たとえば、m = 1 および n = 2 の場合、 反応は A では 1 次で、B では 2 次です。全体的な反応次数は、単純に各反応物の次数の合計です。 ここでの速度則の例では、反応は全体として 3 次です (1 + 2 = 3)。

速度の法則を決定するための一般的な実験的アプローチは、初速度の方法です。 この方法には、異なる初期反応物質濃度を使用して実行される複数の実験試行の反応速度を測定することが含まれます。 これらの試行で測定された速度を比較することにより、反応次数を決定し、その後速度定数を決定することができ、これらを合わせて速度則を定式化するために使用されます。

反応速度則は一部の反応物質に対して分数次数を示す場合があり、1 つの反応物質の濃度が増加すると反応速度が低下する場合、負の反応次数が観察されることがあります。 速度則は実験によってのみ決定され、反応化学量論によって確実に予測されるわけではないことに注意することが重要です。

反応順序は、反応速度と反応物や生成物の濃度の関係を決定します。

<ul style="list-style-type: disc; padding-left: 35px; margin: 0;">
	<li>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、反応速度は全体を通して一定のままです。</li>
	<li>一次反応では、反応速度は反応物質の濃度の変化に直接かつ直線的に比例します。 反応物質の濃度が減少すると、反応速度も比例して減少します。</li>
	<li>二次または高次の反応では、反応速度は反応物の指数関数的値に比例します。 したがって、反応が進行し、反応物質の濃度が減少すると、反応速度は指数関数的に減少します。</li>
</ul>

このテキストは下記から翻案されます <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

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

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 a specific temperature.

The exponents m and n are the reaction orders. They are usually positive integers, but they can also be fractions, negative values, or zero. 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 separate orders, so this example is third order overall.

Rate law values are found by experiment, not by stoichiometry. Scientists change the initial reactant concentrations in several trials and measure the reaction rate. This method, called the method of initial rates, helps determine the reaction orders and then the rate constant.

Some reactions show zero-order behavior. In a zero-order reaction, changes in reactant concentration do not change the rate, so the rate stays constant. In a first-order reaction, the rate changes in direct proportion to the reactant concentration. In second-order and higher-order reactions, the rate depends on the concentration raised to an exponent, so the rate drops more sharply as reactants are used up.

Rate laws can also show fractional orders, and some can even show negative orders. A negative order means that increasing one reactant can decrease the reaction rate. These patterns are useful for describing how reaction rate changes in real experiments. They are not reliably predicted from the reaction equation alone, so the rate law must be determined experimentally.

How Reactant Concentration Sets Reaction Rate

how-reactant-concentration-sets-reaction-rate

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rate law and reaction order

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

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

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key terms and concepts

Learn how rate laws connect reactant concentration to reaction speed, how reaction orders work, and how the method of initial rates is used to find them.

How Reactant Concentration Sets Reaction Rate | 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。

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How Reactant Concentration Sets Reaction Rate

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