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

对于任何反应，反应速率与反应物浓度之间的关系均可通过速率定律或速率方程以数学形式表达。&#160;
在速率定律中，‘k’ 是比例常数，即速率常数，‘n’ 是相对于单一反应物的反应级数，其值通常为整数。对于多反应物反应的速率定律，总反应级数是所有反应物级数之和。
对于每种反应物，反应速率、速率常数、浓度和反应级数均通过实验确定。
反应物的级数通常为0、1或2，根据总反应级数，化学反应可分为零级反应、一级反应或二级反应。
反应速率在整个反应过程中保持不变的单反应物（或单分子）化学反应称为零级反应。在零级反应中，反应物的级数为零，反应物浓度的幂次为零次方。
由于任何数的零次幂都等于一，零级反应的反应速率等于速率常数，因此与反应物浓度无关。
反应速率与反应物浓度成正比的单分子化学反应称为一级反应。一级反应的反应物级数为1，根据速率定律，反应物浓度的幂次为一次方。
由于任何数的 1 次方的值保持不变，一级反应的反应速率直接取决于反应物浓度。随着反应物浓度降低，反应速率以线性方式成比例下降。
反应速率取决于反应物浓度平方的单分子化学反应称为二级反应。随着反应物浓度的降低，反应速率以二次方形式呈指数下降。

速率定律和反应顺序

反应速率受反应物浓度的影响。 速率定律（微分速率定律）或速率方程是描述化学反应速率与反应物浓度关系的数学表达式。


 例如，对于一般反应 aA + bB ⟶产物，其中 a 和 b 是化学计量系数，速率定律可以写为:


 速率 = k[A]m[B]n


 [A]和[B]代表反应物的摩尔浓度，k是速率常数，在特定温度下对特定反应而言是恒定的。


 指数 m 和 n 是反应级数，通常为正整数，但也可以是分数、负值或零。


 速率常数 k 以及反应级数 m 和 n 通过观察反应速率如何随反应物浓度变化而变化而通过实验确定。 速率常数 k 不受反应物浓度影响，但随温度变化。


 速率定律中的反应级数描述了速率对反应物浓度的数学依赖性。 参考一般速率定律（速率 = k[A]m[B]n），反应对于 A 是mth 级反应，对于 B 是 nth 级反应。例如，如果 m = 1 且 n = 2，则 A 中的反应为一级反应，B 中的反应为二级反应。总反应级数是每种反应物的级数之和。 对于此处的速率定律示例，反应整体为三级 (1 + 2 = 3)。


 确定速率定律的常用实验方法是初始速率法。 该方法涉及测量使用不同初始反应物浓度进行的多个实验的反应速率。 比较这些试验的测量速率可以确定反应级数，并随后确定速率常数，它们一起用于制定速率定律。


 对于某些反应物，速率定律可能表现出分数级反应，当一种反应物浓度的增加导致反应速率降低时，有时会观察到负反应级。 值得注意的是，速率定律只能通过实验确定，不能通过反应化学计量可靠预测。


 反应级数决定了反应速率与反应物或产物浓度之间的关系。


 <ul>
 <li>在零级反应中，反应物的浓度对反应速率没有任何影响，反应速率始终保持恒定。</li>
 <li>在一级反应中，反应速率与反应物浓度的变化成直接线性比例。 随着反应物浓度降低，反应速率也成比例降低。</li>
 <li>在二级或更高级反应中，反应速率与反应物的指数值成正比。 因此，随着反应的进行和反应物浓度的降低，反应速率呈指数下降。</li>
 </ul>


 本文改编自 <a href="https://openstax.org/books/chemistry-2e/pages/12-3-rate-laws#57033">Openstax, Chemistry 2e, Section 12.3: Rate Laws

反应速率受反应物浓度的影响。速率定律（微分速率定律）或速率方程是数学表达式……

Education

教育

JoVE Core

Organic Chemistry

有机化学

Unit 1

第一单元

Thermodynamics and Chemical Kinetics

热力学与化学动力学

KEY TERMS AND CONCEPTS

关键术语与概念

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

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

How Solubility Depends on Free Energy

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

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

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...

multi-step reactions

Reaction Mechanisms and Rate-Determining Steps

Chemical reactions can happen in a sequence of steps. A balanced chemical equation shows the reactants and products, but it does not show how the reaction occurs at the molecular level. The reaction mechanism, or reaction path, gives that step-by-step detail. Each step in a mechanism is an elementary reaction. These elementary reactions happen in order, and together they add up to the balanced equation for the overall reaction. In a multistep mechanism, one step is often much slower than the...

bond dissociation energy and activation energy

bond-dissociation-energy-and-activation-energy

How Bond Strength Shapes Reaction Speed

Bond strength and activation energy help explain why organic reactions happen. Bond energy is the energy needed to break a bond homolytically, which means each atom takes one of the shared electrons. When a bond value is given for one specific bond, it is called bond dissociation energy. When it is given for a bond type across many compounds, it is called average bond energy. Bond dissociation energy usually follows a clear pattern. A single bond is weaker than a double bond, and a double bond...

energy diagrams, transition states, and intermediates

energy-diagrams-transition-states-and-intermediates

Reaction Coordinate Diagrams in Chemical Reactions

Reaction coordinate diagrams show how energy changes during a chemical reaction. These free-energy graphs use the horizontal axis to show reaction progress. Points near the reactants look like the reactants, while points near the products look like the products. The peaks on the diagram represent stable structures with measurable lifetimes. Other points on the curve are unstable and cannot be isolated. The high-energy, unstable peak is called the transition state, or activated complex. At the...

predicting reaction outcomes

How Temperature Changes Reaction Rate

Reaction rate and reaction pathway are key ideas in chemical kinetics. Thermodynamics, by contrast, focuses on the state of a system. It describes the properties, behavior, and components of reactants and products. It does not describe the path of the process or the speed of the reaction. Kinetics gives information on the atomic or molecular level, while thermodynamics focuses on the energetics of the reactants and products. Thermodynamics can show what may happen in a reaction, but it does...

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 有机化学（Organic Chemistry）使用简明易懂的动画视频课程解释立体化学、反应和机制的基本概念。 此外，科学家在行动视频展示了相关概念在当今世界各地实验室进行的经典和原创研究实验中的应用。

Introduction to Scalars

Many familiar physical quantities can be specified completely by giving a single number and the appropriate unit. For example, &#34;a class period lasts ...

Introduction to Vectors

To define some physical quantities, there is a need to specify both magnitude as well as direction. For example, when the U.S. Coast Guard dispatches a ...

vector-components-in-the-cartesian-coordinate-system

Vector Components in the Cartesian Coordinate System

Vectors are usually described in terms of their components in a coordinate system. Even in everyday life, we naturally invoke the concept of orthogonal ...

Vector Algebra: Graphical Method

Vectors can be multiplied by scalars, added to other vectors, or subtracted from other vectors. The vector sum of two (or more) vectors is called the ...

Vector Algebra: Method of Components

It is cumbersome to find the magnitudes of vectors using the parallelogram rule or using the graphical method to perform mathematical operations like ...

/files/media/science-education/science-education-thumbs/12613.jpg

Scalar Product (Dot Product)

The scalar multiplication of two vectors is known as the scalar or dot product. As the name indicates, the scalar product of two vectors results in a ...

Vector Product (Cross Product)

Vector multiplication of two vectors yields a vector product, with the magnitude equal to the product of the individual vectors multiplied by the sine of ...

Scalar and Vector Triple Products

Two vectors can be multiplied using a scalar product or a vector product. The resultant of a scalar product is scalar, while with vector products, the ...

/files/media/science-education/science-education-thumbs/14688.jpg

Gradient and Del Operator

In mathematics and physics, the gradient and del operator are fundamental concepts used to describe the behavior of functions and fields in space. The ...

/files/media/science-education/science-education-thumbs/14689.jpg

Divergence and Curl

The divergence of a vector field at a point is the net outward flow of the flux out of a small volume through a closed surface enclosing the volume, as ...

/files/media/science-education/science-education-thumbs/14690.jpg

Second Derivatives and Laplace Operator

The first order operators using the del operator include the gradient, divergence and curl. Certain combinations of first order operators on a scalar or ...

/files/media/science-education/science-education-thumbs/14692.jpg

Line, Surface, and Volume Integrals

A line integral for a vector field is defined as the integral of the dot product of a vector function with an infinitesimal displacement vector along a ...

/files/media/science-education/science-education-thumbs/14693.jpg

Distinguish between scalar and vector quantities and assess which should be used to describe an event.

SC.912.P.12.1

Position and Displacement

The position of an object defines its location relative to a convenient frame of reference at any particular time. A frame of reference is an arbitrary ...

Average Velocity

To calculate the other physical quantities in kinematics, we must introduce the time variable. The time variable allows us not only to state the position ...

Instantaneous Velocity - I

The average velocity during a time interval cannot tell us how fast or in what direction a particle is moving at any given time during the interval. To ...

Instantaneous Velocity - II

Instantaneous velocity is the quantity that measures how fast an object is moving along its path. In other words, the instantaneous velocity of an object ...

Average Acceleration

The importance of understanding acceleration spans our day-to-day experiences, as well as the vast reaches of outer space and the tiny world of subatomic ...

Instantaneous Acceleration

Acceleration is in the direction of the change in velocity, but it is not always in the direction of motion. When an object slows down, its acceleration ...

Kinematic Equations - I

When an object moves with constant acceleration, the velocity of the object changes at a constant rate throughout the motion. The kinematic equations of ...

Kinematic Equations - II

The second kinematic equation expresses the final position of an object in terms of its initial position, the distance traveled with the initial constant ...

Kinematic Equations - III

The first two kinematic equations have time as a variable, but the third kinematic equation is independent of time. This equation expresses final velocity ...

Kinematic Equations: Problem Solving

When analyzing one-dimensional motion with constant acceleration, the problem-solving strategy involves identifying the known quantities and choosing the ...

Free-falling Bodies: Introduction

All objects, neglecting air resistance, fall with the same acceleration towards the Earth&#39;s center due to the force exerted by the Earth&#39;s ...

Free-falling Bodies: Example

An object falling without any air resistance under the influence of gravitational force is said to be in free-fall. For free-falling bodies, the ...

velocity-and-position-by-graphical-method

Velocity and Position by Graphical Method

Velocity and position can be calculated from the known function of acceleration as a function of time. The total area under the acceleration-time graph ...

Non-uniform Circular Motion

In&#160;uniform circular motion, the particle executing circular motion has a constant speed, and the circle is at a fixed radius. However, not all ...

Velocity and Position by Integral Method

If acceleration as a function of time is known, then velocity and position functions can be derived using integral calculus. For constant acceleration, ...

Relative Velocity in One Dimension

The understanding of the concept of reference frames is essential to discuss relative motion in one or more dimensions. When we say that an object has a ...

Position and Displacement Vectors

To describe the motion of an object, one should first be able to describe its position (where it is at any particular time). More precisely, the position ...

Relative Velocity in Two Dimensions

Relative velocity is the velocity of an object as observed from a particular reference frame, or the velocity of one reference frame with respect to ...

average-and-instantaneous-velocity-vectors

Average and Instantaneous Velocity Vectors

To calculate other physical quantities in kinematics, the time variable must be introduced. The time variable not only allows us to state where an object ...

Acceleration Vectors

In everyday conversation, accelerating means speeding up. Acceleration is a vector in the same direction as the change in velocity, &#916;v, therefore the ...

Direction of Acceleration Vectors

Acceleration occurs when velocity changes in magnitude (an increase or decrease in speed), direction, or both. Although acceleration is in the direction ...

Projectile Motion

An object thrown in the air follows a parabolic path under the influence of Earth&#39;s gravitational force. The motion of such an object is called ...

/files/media/science-education/science-education-thumbs/12634.jpg

Projectile Motion: Equations

Projectile motion is commonly observed in our day-to-day life. For example, a basketball thrown by a player, an arrow shot from a bow, and kids jumping ...

Projectile Motion: Example

The theory of projectile motion is very useful for players of several sports to improve their performance. For example, a javelin thrower needs to throw ...

Uniform Circular Motion

Uniform circular motion is a specific type of motion in which an object travels in a circle with a constant speed. For example, any point on a propeller ...

Analyze the motion of an object in terms of its position, velocity, and acceleration (with respect to a frame of reference) as functions of time.

SC.912.P.12.2

Newton's First Law: Introduction

Motion draws our attention. Motion itself can be beautiful, causing us to marvel at the forces needed to create spectacular sights, such as that of a ...

Newton's First Law: Application

Experience suggests that an object at rest remains at rest if left alone, and that an object in motion tends to slow down and stop unless some effort is ...

Internal and External Forces

Newton&#39;s first law states that a net external force causes a change in motion. External forces act on an object or system, originating outside of the ...

Newton's Second Law

Newton&#39;s second law is closely related to his first law of motion. It mathematically gives the cause-and-effect relationship between force and changes ...

Newton's Third Law: Introduction

Whenever one body exerts a force on a second body, the first body experiences a force equal in magnitude and opposite in direction, to the force that it ...

Newton's Third Law: Examples

Newton&#39;s third law states that every action has an equal and opposite reaction. Consider a swimmer pushing off the side of a pool. They push against ...

Inertial Frames of Reference

Newton&#8217;s first law is usually considered to be a statement about reference frames. It provides a method for identifying a special type of reference ...

Non-inertial Frames of Reference

A reference frame accelerating or decelerating relative to an inertial frame is a non-inertial frame. To help understand this, consider what taking off in ...

first-law-particles-in-one-dimensional-equilibrium

First Law: Particles in One-dimensional Equilibrium

Newton&#39;s first law of motion states that a body at rest remains at rest, or if in motion, remains in motion at constant velocity, unless acted on by a ...

first-law-particles-in-two-dimensional-equilibrium

First Law: Particles in Two-dimensional Equilibrium

Recall that a particle in equilibrium is one for which the external forces are balanced. Static equilibrium involves objects at rest, and dynamic ...

Second Law: Motion under Same Force

Newton&#39;s laws can be applied to bodies at rest and bodies in motion. Newton&#39;s first law is applied to bodies in equilibrium, whereas the second ...

second-law-motion-under-same-acceleration

Second Law: Motion under Same Acceleration

Newton&#39;s second law of motion applies to bodies moving under the same acceleration. For example, when a baggage tractor pulls luggage carts, each cart ...

Interpret and apply Newton's three laws of motion.

SC.912.P.12.3

Gravitation

In the years before Newton, a general belief prevailed that different laws governed objects in the sky than objects on Earth. When Kepler wrote down the ...

/files/media/science-education/science-education-thumbs/14716.jpg

Newton's Law of Gravitation

Our everyday observation tells us that all objects close to the Earth naturally tend to fall to the ground. Early philosophers assumed that this downward ...

gravitation-between-spherically-symmetric-masses

Gravitation Between Spherically Symmetric Masses

The gravitational potential energy between two spherically symmetric bodies can be calculated from the masses and the distance between the bodies, ...

/files/media/science-education/science-education-thumbs/14717.jpg

Gravity between Spherical Bodies

Newton&#39;s law of gravitation describes the gravitational force between any two point masses. However, for extended spherical objects like the Earth, ...

Describe how the gravitational force between two objects depends on their masses and the distance between them.

SC.912.P.12.4

Linear Momentum

The term momentum is used in various ways in everyday language, most of which are consistent with the precise scientific definition. Generally, momentum ...

Apply the law of conservation of linear momentum to interactions, such as collisions between objects.

SC.912.P.12.5

A. Motion can be measured and described qualitatively and quantitatively. Net forces create a change in motion. When objects travel at speeds comparable to the speed of light, Einstein's special theory of relativity applies.

B. Momentum is conserved under well-defined conditions. A change in momentum occurs when a net force is applied to an object over a time interval.

C. The Law of Universal Gravitation states that gravitational forces act on all objects irrespective of their size and position.

D. Gases consist of great numbers of molecules moving in all directions. The behavior of gases can be modeled by the kinetic molecular theory.

E. Chemical reaction rates change with conditions under which they occur. Chemical equilibrium is a dynamic state in which forward and reverse processes occur at the same rates.

How Reactant Concentration Sets Reaction Rate

Description

Transcript

More videos by Standards