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

반응 속도는 대체로 반응물의 농도에 따라 달라집니다. 모든 반응에서 반응 속도와 반응물 농도 사이의 관계는 속도 법칙 또는 속도 방정식을 사용하여 수학적으로 표현될 수 있습니다. 속도 법칙에서 k는 비례 상수 또는 속도 상수이며 n은 단일 반응물에 대한 반응 차수로 값은 대체로 정수입니다.

다중 반응물 반응에 대한 속도 법칙에서 전체 반응 차수는 모든 반응물 차수의 합입니다. 각 반응물에 대한 반응 속도, 속도 상수, 농도 및 반응 차수는 모두 실험적으로 결정됩니다. 속도 법칙은 이러한 모든 매개 변수 간의 관계를 나타냅니다.

개별 반응물의 차수는 일반적으로 0, 1 또는 2의 값을 가지며, 전체 반응 차수에 따라 화학 반응을 0차, 1차 반응 또는 2차 반응으로 분류할 수 있습니다. 반응 속도가 반응 지속 기간 내내 일정하게 유지되는 단일 반응물 또는 비분자 화학 반응은 0차 반응입니다. 0차 반응에서 반응물의 차수는 0이고 속도 법칙에 따라 반응물 농도는 0차 제곱으로 상승합니다.

0차 제곱으로 상승된 숫자의 값이 1이기때문에 0차 반응의 반응 속도는 속도 상수와 같으며 따라서 반응물 농도와 무관합니다. 따라서 0차 반응에서는 반응물의 농도가 낮아지더라도 반응 속도가 느려지지 않습니다. 반응 속도가 반응물의 농도에 정비례하는 단분자 화학 반응은 1차 반응입니다.

1차 반응에 대한 반응물의 차수는 1이고 속도 법칙에 따라 반응물의 농도가 1제곱으로 올라갑니다. 1의 제곱으로 상승한 숫자의 값은 그대로 유지되므로 1차 반응의 반응 속도는 직접적으로 반응물 농도에 따라 달라집니다. 반응물의 농도가 감소하면 반응 속도는 선형적으로 비례하여 감소합니다.

반응 속도가 반응물 농도의 두제곱에 따라 달라지는 단분자 화학 반응은 2차 반응입니다. 반응물은 차수가 2이고 농도는 2 제곱으로 상승합니다. 따라서 2차 반응의 반응 속도는 반응물 농도의 두 제곱에 직접 의존합니다.

반응물의 농도가 감소하면 반응 속도는 2차 방식으로 기하급수적으로 감소합니다.

농도와 비율의 법칙

반응 속도는 반응물의 농도에 영향을 받습니다. 속도 법칙(미분 속도 법칙) 또는 속도 방정식은 화학 반응 속도와 반응물의 농도 사이의 관계를 설명하는 수학적 표현입니다.

예를 들어, a와 b가 화학양론적 계수인 일반 반응 aA + bB ⟶ 곱에서 속도 법칙은 다음과 같이 작성할 수 있습니다.

 <img alt="Eq1" src="/files/ftp_upload/11375/11375_Equation_1.png" style="height: 50px;" />

[A]와 [B]는 반응물의 몰 농도를 나타내고, k는 특정 온도에서 특정 반응에 특정한 속도 상수입니다.

지수 m과 n은 반응 차수이며 일반적으로 양의 정수이지만 분수, 음수 또는 0일 수도 있습니다.

속도 상수 k와 반응 차수 m, n은 반응물의 농도가 변함에 따라 반응 속도가 어떻게 변하는지 관찰하여 실험적으로 결정됩니다. 속도 상수 k는 반응물 농도와 무관하지만 온도에 따라 달라집니다.

속도 법칙의 반응 차수는 반응물 농도에 대한 속도의 수학적 의존성을 설명합니다. 일반 속도 법칙(rate = k[A]^m[B]^n)을 참조하면 반응은 A에 대해 m차이고 B에 대해 n차입니다. 예를 들어 m = 1이고 n = 2인 경우 반응은 A에서는 1차이고 B에서는 2차입니다. 전체 반응 차수는 단순히 각 반응물의 차수의 합입니다. 여기에 있는 속도법칙의 경우 반응은 전체적으로 3차입니다(1 + 2 = 3).

비율 법칙을 결정하는 일반적인 실험적 접근 방식은 초기 비율 방법입니다. 이 방법에는 다양한 초기 반응물 농도를 사용하여 수행된 여러 실험 시도에 대한 반응 속도를 측정하는 작업이 포함됩니다. 이러한 시도에 대해 측정된 속도를 비교하면 반응 차수를 결정할 수 있으며, 이어서 속도 법칙을 공식화하는 데 함께 사용되는 속도 상수를 결정할 수 있습니다.

속도 법칙은 일부 반응물에 대해 분수 차수를 나타낼 수 있으며, 한 반응물의 농도가 증가하면 반응 속도가 감소할 때 음의 반응 차수가 때때로 관찰됩니다. 속도 법칙은 실험에 의해서만 결정되며 반응 화학양론으로는 확실하게 예측할 수 없다는 점에 유의하는 것이 중요합니다.

반응 차수는 반응 속도와 반응물 또는 생성물의 농도 사이의 관계를 결정합니다.

<ol style="list-style-type: disc;">
	<li>0차 반응에서는 반응물의 농도가 반응 속도에 아무런 영향을 미치지 않으며 반응 속도는 전체적으로 일정하게 유지됩니다.</li>
	<li>1차 반응에서 반응 속도는 반응물 농도 변화에 정비례하고 선형적으로 비례합니다. 반응물 농도가 감소함에 따라 반응 속도도 비례적으로 감소합니다.</li>
	<li>2차 또는 고차 반응에서 반응 속도는 반응물의 지수 값에 비례합니다. 따라서 반응이 진행되면서 반응물의 농도가 감소할수록 반응속도는 기하급수적으로 감소합니다.</li>
</ol>

이 문서는 에서 발췌되었습니다 <a href="https://openstax.org/books/chemistry-2e/pages/12-3-rate-laws#57033">Openstax, Chemistry 2e, Section 12.3: Rate Laws</a>.

반응 속도는 반응물의 농도에 영향을 받습니다. 속도 법칙 (미분 속도 법칙) 또는 속도 방정식은 수학 표현입니다 ...

Education

교육

JoVE Core

Chemistry

화학

하나

Chemical Kinetics

화학 반응 속도론

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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

Measuring Reaction Rates

Measuring reaction rates shows how fast reactants are used up or products are formed over time. The rate of reaction is the change in the amount of a reactant or product per unit time. Because of that, scientists measure how a property changes as the reaction proceeds and connect that change to reactant or product amounts. For reactions that make or use a gas, the rate can be followed by changes in volume or pressure. A rate expression is the mathematical way to write how concentration changes...

measuring reaction rates

Tracking Reaction Kinetics with Light and Pressure

Reaction kinetics can be tracked with polarimetry, spectrometry, and pressure measurements. These methods let scientists follow a reaction without disturbing the sample. They also help determine how reactant or product concentrations change over time. Polarimetry is used for optically active substances. These substances rotate the plane of polarized light, which is called optical rotation. The effect comes from molecular structure. Normal monochromatic light is unpolarized, but after it passes...

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...

determining order of reaction

Finding Rate Law from Initial Rates

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

Integrated rate laws connect reaction concentration to time. They help show how much reactant or product is present after a certain period. They can also help estimate how long a reaction must run to reach a given extent. A common use is finding how long radioactive material must be stored before its radioactivity drops to a safe level. These equations come from the differential rate law after it is integrated with respect to time. For a first-order reaction, where rate = k[A], the integrated...

half-life of a reaction

Reaction Half-Life in Kinetics

Reaction half-life is the time needed for half of a reactant to be consumed. After each half-life, half of the remaining reactant is used up. A hydrogen peroxide decomposition example shows this pattern clearly. The concentration drops from 1.000 M to 0.500 M in the first 6.00 hours, then to 0.250 M in the next 6.00 hours, and then to 0.125 M in the third period. Each later 6.00-hour interval removes half of what is left. For first-order reactions, the half-life does not depend on the reactant...

temperature dependence on reaction rate

Collision Theory and Reaction Speed

Collision theory explains why reaction speed depends on how particles collide. Atoms, molecules, or ions must come close together before they can react. The theory says the reaction rate depends on the collision rate, the orientation of the colliding species, and whether the collision has enough energy for bonds to change. A gas-phase reaction between carbon monoxide and oxygen shows why orientation matters. The molecules can collide in more than one way. If the oxygen side of carbon monoxide...

arrhenius plots

Determining Activation Energy from Temperature

The Arrhenius equation links activation energy and the rate constant, k, for chemical reactions. It is written as k = Ae−Ea/RT. In this equation, R is the ideal gas constant with a value of 8.314 J/mol·K, T is the temperature on the kelvin scale, Ea is the activation energy in J/mole, e is the constant 2.7183, and A is the frequency factor. The frequency factor depends on collision frequency and the orientation of reacting molecules. Experimental kinetic data can be used to find the activation...

reaction mechanisms

Elementary Steps in Reaction Mechanisms

Chemical reactions can happen in steps, and a balanced equation does not show the full path at the molecular level. A reaction mechanism, also called a reaction path, gives the step-by-step process that explains how reactants become products. The decomposition of ozone is one example of a reaction that can be described by a sequence of steps. Each step in a mechanism is an elementary reaction. These elementary reactions happen in order, and when they are added together, they give the balanced...

rate-determining steps

Reaction Bottlenecks in Chemical Kinetics

Reaction bottlenecks help explain rate-determining steps in multistep reaction mechanisms. In a mechanism with several elementary steps, one step is often much slower than the others. That slowest step is called the rate-limiting step, or rate-determining step. A reaction cannot move faster than its slowest step, so this step controls the overall reaction rate. The idea is like traffic on a four-lane freeway with one lane closed. Cars can only move as fast as the bottleneck allows. In the same...

catalysis

Catalyst Action in Reaction Rates

Catalysts change the rate of a chemical reaction by giving it a faster path. A catalyst increases reaction rate without being consumed during the process. Its effect is often explained with reaction mechanisms and energy diagrams. For an endothermic reaction, the reactants and products start and end at the same energies in both cases. The uncatalyzed path is a one-step mechanism with one transition state. The catalyzed path follows a different mechanism with two transition states and a lower...

enzymes

Enzyme Action and Inhibition

Enzymes are biological catalysts that speed up many reactions in living organisms. They help control cellular metabolism by lowering the activation energy needed for biochemical reactions. When activation energy drops, reaction rates can increase. Enzyme problems can also lead to serious disease. A genetic abnormality that causes G6PD, or glucose-6-phosphate dehydrogenase, deficiency can disrupt the pathway that supplies NADPH to cells. In red blood cells, this can reduce glutathione and...

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

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IPC.7.D

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IPC.7.E

Science concepts. The student knows that relationships exist between the structure and properties of matter. The student is expected to:

Reaction Order from Concentration

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