Name: measuring reaction rates
Uploaded: 2020-09-24T15:06:50.000Z
Duration: 2 min 53 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.7

IPC.7.F

Reaction Rate

화학 반응에는 반응물을 생성물로 변환하는 화학적 과정이 포함됩니다. 반응이 진행되면 반응물의 농도는 낮아지고 생성물의 농도는 증가합니다. 반응물 및 생성물 농도의 이러한 분산은 시간의 함수로 그래프에 표시할 수 있습니다.

반응이 진행되는 속도를 반응 속도라고 합니다. 반응 속도는 반응물의 소멸 속도 또는 생성물의 형성 속도를 측정하고 초당 몰 농도 단위로 표시합니다. 평균 반응 속도는 특정 기간 동안 반응물 또는 생성물의 농도 변화를 통해 계산할 수 있습니다.

몰 농도 값은 괄호로 표시되고 t는 기간을 나타내며 델타 기호는 변화'를 나타냅니다. 화학 반응 중에 반응물이 고갈되기 때문에 반응물의 농도 변화 값은 항상 음수입니다. 따라서 반응물 측면에서 계산된 반응 속도는 음의 부호로 보완되어 전체 값은 양수로 됩니다.

반응 속도는 반응의 전 기간에 균일하지 않습니다. 반응이 시작될 때 즉 시간 제로'일 때의 속도를 초기 반응 속도라고 합니다. 반응물의 농도가 감소하면 반응 속도가 감소하거나 반응이 느려집니다.

주어진 시점에서의 반응 속도 또는 순간 반응 속도는 관심하는 시점에 반응 곡선에 그려진 탄젠트의 기울기를 계산하여 측정할 수 있습니다. 기울기 값 또는 특정 시점에서의 순간 속도는 모든 반응물 및 생성물에서 동일합니다. 화학 반응의 반응 속도는 또한 반응물과 생성물의 실제 화학당량 계수를 반영합니다.

따라서, A의 c 몰이 B의 b 몰과 반응하여 C의 c 몰과 D의 d 몰을 생성하는 모든 균형 반응의 경우 마이너스 1/a 곱하기 시간에 따른 반응물 A의 농도 변화가 마이너스 1/b 곱하기 시간에 따른 반응물 B의 농도 변화와 같다는 일반적인 공식을 사용하여 반응 속도를 표현하고 계산할 수 있습니다. 이 값은 1/c 곱하기 생성물 C의 시간에 따른 농도 변화, 1/d 곱하기 생성물 D의 시간에 따른 농도 변화와 같습니다. 반응 속도를 결정하는 것은 약제나 촉매, 또는 합성 반응이 얼마나 빨리 작용하는지 이해하는 데 도움이 되는 화학적 운동학을 연구하는 데 있어 기본적이며 이를 통해 약물이 기능을 더 잘 발현하고 최적화될 수 있도록 도와줍니다.

반응속도

반응 속도는 단위 시간당 반응물 또는 생성물의 양의 변화입니다. 따라서 반응 속도는 반응물 또는 생성물 양과 관련될 수 있는 일부 특성의 시간 의존성을 측정하여 결정됩니다. 예를 들어, 기체 물질을 소비하거나 생성하는 반응 속도는 부피나 압력의 변화를 측정하여 편리하게 결정됩니다.

시간이 지남에 따라 반응물과 생성물의 농도 변화를 수학적으로 표현한 것이 반응의 속도 표현입니다. 괄호는 몰 농도를 나타내고 기호 델타(Δ)는 "변화"를 나타냅니다.

예를 들어, 수용액 내 과산화수소(H_2O_2)의 농도는 다음 방정식에 따라 분해되면서 시간이 지남에 따라 천천히 변합니다.

<img alt="Eq1" src="/files/ftp_upload/11373/11373_Equation_1.png" style="height: 50px;" />

과산화수소가 분해되는 속도는 농도 변화율로 표현될 수 있습니다.

<img alt="Eq2" src="/files/ftp_upload/11373/11373_Equation_2.png" style="height: 70px;" />

따라서 [H_2O_2]_t_1은 시간 t_1에서의 과산화수소의 몰 농도를 나타냅니다. 마찬가지로 [H_2O_2]_t_2는 이후 시간 t_2에서의 과산화수소의 몰 농도를 나타냅니다. Δ[H_2O_2]는 Δt(즉, t_2 − t_1) 시간 간격 동안 과산화수소의 몰 농도 변화를 나타냅니다. 반응이 진행됨에 따라 반응물 농도가 감소하므로 Δ[H_2O_2]는 음의 양입니다. 반응 속도는 일반적으로 양수이므로 농도의 음수 변화에 -1을 곱합니다.

평균반응속도와 순간반응속도

반응 속도는 시간에 따라 달라지며 반응이 진행됨에 따라 감소합니다. 시간 간격에 따른 평균 반응 속도는 반응 속도가 변화하는 이 기간의 시작과 끝의 농도를 사용하여 계산할 수 있습니다. 특정 시간에 반응이 진행되는 속도를 순간 속도라고 합니다. 반응이 시작되는 "0시간"에서의 반응의 순간 속도가 초기 속도입니다.

반응의 순간 속도는 두 가지 방법 중 하나로 결정될 수 있습니다. 실험 조건이 짧은 시간 간격에 걸쳐 농도 변화를 측정할 수 있는 경우 평균 속도 계산은 순간 속도에 대한 합리적으로 좋은 근사치를 제공합니다. 대안으로 그래픽 절차를 사용할 수도 있습니다. 예를 들어, 과산화수소 분해의 예에서 시간에 따른 과산화수소의 농도를 그래프로 나타내면, 그 시점의 곡선에 그려진 접선의 기울기로부터 언제든지 't' 시점의 H_2O_2의 순간 분해 속도를 계산할 수 있습니다.

<img alt="Image1" src="/files/ftp_upload/11373/11373_Image_1.png" style="height: 300px;" />

이 그래프는 1.000M H_2O_2 용액에 대한 농도 대 시간의 플롯을 보여줍니다. 어느 시점의 비율은 그 시점의 곡선에 접하는 선의 기울기의 음수와 같습니다. 접선은 t = 0h("초기 속도") 및 t = 12h(12시간의 "순간 속도")에 표시됩니다.

상대적 반응 속도

반응 속도는 반응물이나 생성물의 농도 변화로 표현될 수 있습니다. 주어진 반응에 대해 이러한 속도 표현은 모두 반응 화학양론에 따라 서로 관련됩니다. 일반 반응 aA ⟶ bB의 속도는 A 농도의 감소 또는 B 농도의 증가로 표현될 수 있습니다. 이 두 속도 표현은 반응의 화학량론과 관련되어 있습니다. 여기서:

<img alt="Eq3" src="/files/ftp_upload/11373/11373_Equation_3.png" style="height: 70px;" />

두 가지 양 변화의 반대 부호(생성물 양이 증가하는 동안 반응물 양이 감소함)를 설명하기 위해 음수 부호가 요소로 포함되었습니다.

이 문서는 에서 발췌되었습니다 <a href="https://openstax.org/books/chemistry-2e/pages/12-introduction">Openstax, Chemistry 2e, Chapter 12 Introduction</a> and <a href="https://openstax.org/books/chemistry-2e/pages/12-1-chemical-reaction-rates#12163">Openstax, Chemistry 2e, Section 12.1: Chemical Reaction Rates.</a>

반응 속도는 단위 시간당 반응물 또는 생성물의 양의 변화입니다. 따라서 반응 속도는 시간을 측정하여 결정됩니다 ...

Education

교육

JoVE Core

Chemistry

화학

하나

Chemical Kinetics

화학 반응 속도론

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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 over time. In this expression, brackets mean molar concentration, and the delta symbol means change in amount.

Hydrogen peroxide provides a clear example. As H2O2 decomposes in water, its concentration slowly decreases with time. The reaction rate can be written as the rate of change of the H2O2 concentration. If the concentration at time t1 is compared with the concentration at a later time t2, the change in concentration over the time interval Δt is found.

Because the reactant concentration goes down, Δ[H2O2] is negative. Reaction rates are reported as positive values, so the negative sign is reversed by multiplying by -1. This keeps the reaction rate positive even when the reactant amount is falling.

Reaction rates are not constant. They usually change as the reaction continues, so an average reaction rate is calculated over a time interval using the starting and ending concentrations. The rate at one exact moment is the instantaneous rate, and the instantaneous rate at time zero is the initial rate.

Instantaneous rate can be estimated in two ways. If concentration changes can be measured over very short time intervals, the average rate gives a good approximation. A graph can also be used. When concentration is plotted against time, the instantaneous rate at a given time equals the negative slope of a tangent line to the curve. In the hydrogen peroxide example, tangents can be drawn at t = 0 h for the initial rate and at t = 12 h for the instantaneous rate at 12 h.

The rate of a reaction can be written using either a reactant or a product. For a general reaction aA → bB, the decrease in A and the increase in B are linked by the reaction stoichiometry. The two rate expressions are related by that stoichiometry, and a negative sign is included to account for the reactant decreasing while the product increases.

Measuring Reaction Rates

reaction rate

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...

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

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 reaction rates are measured using concentration, volume, pressure, average rate, and instantaneous rate with the hydrogen peroxide example.

Measuring Reaction Rates | JoVE K12

chemistry

JoVE Core 화학은 간결하고 이해하기 쉬운 애니메이션을 통해 일반 화학 개념을 설명합니다. 또한, 과학자가 직접 고전실험과 연구실험을 진행하는 실사 영상을 제공합니다.

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North Carolina K-12 Science Standard Course of Study

9-12

Matter and its Interactions

PS.Chm.5.1

Pennsylvania State Academic Standards

Physical Science

Chemical Reactions

3.2.9-12.D

3.2.9-12.E

Louisiana Student Standards for Science

Matter And Its Interactions

HS-PS1-4

HS-PS1-6

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Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

Virginia  Standards of Learning

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CH.7

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Minnesota Academic Standards in Science

3.2.1 9C.3.1.1.2

Arizona Science Standards

HS.P1

HS.P1U1.3

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

Matter and Its Interactions

HS-PS1-5

Alabama Course of Study Science

Matter and Its Interactions: Energy

9-12.C.3.3.d

Next Generation Science Standards

Florida Department of Education

SC.912.P.12

SC.912.P.12.12

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New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-5.

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phase-transitions-sublimation-and-deposition

Phase Transitions: Sublimation and Deposition

Some solids can transition directly into the gaseous state, bypassing the liquid state, via a process known as sublimation. At room temperature and ...

Melting Points

Melting Points in Organic Chemistry
The melting point of a compound is the temperature at which the solid phase transitions into the liquid phase at a ...

Boiling Points

Source: Lara Al Hariri at the University of Massachusetts Amherst, MA, USA

	Preparation of the LaboratoryExpand
	Here, we show the laboratory preparation ...

Explain how physical and chemical properties of substances are related to their usage in everyday life such as in sunscreen, cookware, industrial applications, and fuels.

IPC.7.C

Emission Spectra

When solids, liquids, or condensed gases are heated sufficiently, they radiate some of the excess energy as light. Photons produced in this manner have a ...

Metal Flame Emission

Metal Flame Emission
Flame testing is an analytical technique where a sample is placed in a flame, and the characteristic flame color is used to identify ...

Atomic Orbitals

An atomic orbital represents the three-dimensional regions in an atom where an electron has the highest probability to reside. The radial distribution ...

The Pauli Exclusion Principle

The arrangement of electrons in the orbitals of an atom is called its electron configuration. We describe an electron configuration with a symbol that ...

The Energies of Atomic Orbitals

In an atom, the negatively charged electrons are attracted to the positively charged nucleus. In a multielectron atom, electron-electron repulsions are ...

Explain how electrons can transition from a high energy level to a low energy state, emitting photons at different frequencies for different energy transitions.

IPC.7.D

The de Broglie Wavelength

In the macroscopic world, objects that are large enough to be seen by the naked eye follow the rules of classical physics. A billiard ball moving on a ...

Explain how atomic energy levels and emission spectra present evidence for the wave particle duality.

IPC.7.E

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

Measuring Reaction Rates

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