Name: stoichiometry, rates, and equilibrium
Uploaded: 2023-04-30T18:28:32.000Z
Duration: 2 min 26 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.8

IPC.8.A

Chemical Reactions

水素ガスの燃焼など、バランスの取れた化学反応を考えてみましょう。ここで、反応物と生成物(H2、O2、およびH2O)の間の量的関係は、H2の2つの分子がO2の1つの分子と反応してH2Oの2つの分子を生成することです。この定量的な関係は、化学量論として知られています。
化学反応では、反応物が互いに相互作用して生成物を形成します。完全に消費された反応物が制限反応物であり、制限反応物と完全に反応するために必要以上の量で存在する反応物が過剰反応物です。
化学反応には、反応物が生成物に化学変換されることが含まれます。反応が進行するにつれて、反応物の濃度は減少し、生成物の濃度は増加します。この反応物と生成物の濃度の変動は、時間の関数としてグラフにプロットできます。
反応が進行する速度を反応速度といいます。これは、反応物の消失速度または生成物の出現速度を測定し、モル濃度/秒の単位で表されます。
可逆的な化学反応とは、反応物の生成物への変換と生成物の反応物への再変換が同時に起こる反応です。反応物と生成物の間の二重矢印は、その可逆的な性質を示しています。
生成物の形成速度、または順反応の速度が反応物の形成速度、または逆反応の速度と等しいとき、化学平衡が達成されます。
平衡定数の発現は、平衡状態における反応物AとBに対する生成物CとDのモル濃度として記述され、それぞれがそれぞれの化学量論的係数に上昇します。解くと、式は平衡定数 Kc に等しくなります。
同じ形式の式は、任意の濃度の反応物と生成物についても書くことができ、計算された量は反応商Q cとして知られています。

化学反応

平衡化学方程式は、化学変化に関与する反応物と生成物の化学式の情報を提供します。 反応の化学量論は、所望の量の生成物を生成するためにどのくらいの反応物が必要か、または場合によっては、特定の量の反応物からどのくらいの量の生成物が生成されるかを予測するのに役立ちます。

平衡化学方程式で表される反応物と生成物の相対量は、化学量論量と呼ばれることがよくあります。 しかし、実際には、反応物は常に平衡式で示される化学量論量で存在するとは限りません。

化学反応では、最初に消費されて生成物の量を制限する反応物が制限反応物となり、他の物質が過剰反応物となります。 他の反応物の生成物への完全な変換を確実にするために、1 つ以上の反応物を過剰に使用することがよくあります。

次の方程式で表される水の生成反応を考えてみましょう。

化学量論は、2 モルの水素と 1 モルの酸素が反応して 2 モルの水が生成されることを示します。 つまり、水素と酸素は 2:1 の比率で結合します。

5 モルの水素と 2 モルの酸素が存在すると想像してください。 反応物の比率は 5:2 (または 2.5:1) となり、化学量論比の 2:1 より大きくなります。 したがって、水素が過剰反応物で、酸素が制限反応物となります。 供給された酸素 (2 mol) がすべて反応すると、供給された 5 mol の水素のうち 4 mol が消費され、1 mol の水素が未反応のまま残ります。 提供された各反応物のモル量を計算し、それらを平衡化学方程式で表される化学量論量と比較することは、制限反応物と過剰反応物を特定する 1 つの方法です。

反応速度は、単位時間あたりの反応物または生成物の量の変化です。 したがって、反応速度は、反応物または生成物の量に関連する可能性のあるいくつかの特性の時間依存性を測定することによって決定されます。

化学反応の速度は、時間の関数としての反応物と生成物の濃度の変化としてグラフにプロットできます。

可逆化学反応は、順方向 (左から右) と逆方向 (右から左) の両方の方向に進行する化学プロセスを表します。 可逆反応の状態は、その反応商 (Q) を評価することで簡単に評価できます。 可逆反応の場合、

反応商は、平衡方程式の化学量論から直接導出されます。

ここで、下付き文字 c は、式でのモル濃度の使用を示します。

順反応と逆反応の速度が等しい場合、反応物と生成物種の濃度は時間が経っても一定のままであり、系は平衡状態にあります。 反応の可逆性を強調するために、特別な二重矢印が使用されています。

このテキストは OpenStax Chemistry 2e, Section 4.3: Reaction Stoichiometry; Section 4.4: Reaction Yield; Section 12.1: Chemical Reaction Rates; Section 13.1 Chemical Equilibria, Section 13.2 Equilibrium Constants.

平衡化学方程式は、化学変化に関与する反応物と生成物の化学式の情報を提供します。ある。。。

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

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 called stoichiometric amounts.

In real reactions, reactants are not always present in the exact amounts shown by the equation. The limiting reactant is the substance that gets used up first. It limits how much product can form. The other substance is the excess reactant. Extra reactant is often added so the other reactant can be fully converted into product.

Water formation is a clear example. The balanced equation shows that 2 moles of hydrogen react with 1 mole of oxygen to make 2 moles of water. This is a 2:1 ratio. If 5 moles of hydrogen and 2 moles of oxygen are available, the ratio is 5:2, or 2.5:1. Hydrogen is then in excess, and oxygen is the limiting reactant. All 2 moles of oxygen use 4 moles of hydrogen, leaving 1 mole of hydrogen unreacted.

Reaction rate is the change in the amount of a reactant or product per unit time. Scientists find reaction rates by measuring how a property changes over time if that property can be linked to reactant or product amounts. A rate graph can show how reactant and product concentrations vary with time.

Some reactions are reversible, which means they can proceed in both the forward and reverse directions. The reaction quotient, Q, helps assess the status of a reversible reaction. It is based on the stoichiometry of the balanced equation, and the subscript c shows that molar concentrations are used in the expression. When the forward and reverse rates are equal, concentrations stay constant and the system is at equilibrium. A double arrow is used to show that the reaction is reversible.

Stoichiometry, Rates, and Equilibrium

chemical reactions

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

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...

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 balanced equations, limiting reactants, reaction rates, and equilibrium help predict product formation and track chemical change in high school chemistry.

Stoichiometry, Rates, and Equilibrium | 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。

IPC.8.B

Louisiana Student Standards for Science

Chemistry

Matter And Its Interactions

HS-PS1-6

Tennessee Academic Standards

Matter and Its Interactions

CHEM1.PS1.3

CHEM1.PS1.4

Virginia  Standards of Learning

HIgh School

CH.3

CH.3.f

Florida Department of Education

Physical Science

SC.912.P.10

SC.912.P.10.6

SC.912.P.10.12

SC.912.P.12

SC.912.P.12.12

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

C-PS1-6

A balanced chemical equation provides the information of chemical formulas of the reactants and products involved in the chemical change. A ...

Enthalpy and Heat of Reaction

Combustion, commonly known as burning, is a reaction in which a substance reacts with an oxidizing agent, which in most cases is molecular oxygen, to ...

Oxidation-Reduction Reactions

Oxidation&ndash;Reduction Reactions

Earth&rsquo;s atmosphere contains about 20% molecular oxygen, O2, a chemically reactive gas that plays an essential ...

Oxidation Numbers

In redox reactions, the transfer of electrons occurs between reacting species. Electron transfer is described by a hypothetical number called the ...

Acids, Bases and Neutralization Reactions

An acid-base reaction is one in which a hydrogen ion, H+, is transferred from one chemical species to another. Such reactions are of central importance to ...

combustion-energy-a-measure-of-stability-in-alkanes-and-cycloalkanes

Combustion Energy: A Measure of Stability in Alkanes and Cycloalkanes

The low reactivity in alkanes can be attributed to the non-polar nature of C&#8211;C and C&#8211;H &#963; bonds. Alkanes, therefore, were&#160; initially ...

Investigate how changes in properties are indicative of chemical reactions such as hydrochloric acid with a metal, oxidation of metal, combustion, and neutralizing an acid with a base.

Balancing Redox Equations

Electrochemistry is the science involved in the interconversion of electrical and chemical reactions. Such reactions are called reduction-oxidation, or ...

chemical-equilibria-redefining-equilibrium-constant

Chemical Equilibria: Redefining Equilibrium Constant

Recall that the solubility of a sparingly soluble salt increases with the addition of an inert salt in a phenomenon known as the salt effect.
The extent ...

Factors Affecting Activity Coefficient

The activity coefficient of an ion depends on the ionic strength of the solution.
As indicated by the Debye&#8211;H&#252;ckel theory, when the ionic ...

Thermochemical Equations

For a chemical reaction (the system) carried out at constant pressure &ndash; with the only work done caused by expansion or contraction &ndash; the ...

Develop and use models to balance chemical equations and support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

Nuclear Fission

Many heavier elements with smaller binding energies per nucleon can decompose into more stable elements that have intermediate mass numbers and larger ...

Nuclear Power

Controlled nuclear fission reactions are used to generate electricity. Any nuclear reactor that produces power via the fission of uranium or plutonium by ...

Nuclear Fusion

The process of converting very light nuclei into heavier nuclei is also accompanied by the conversion of mass into large amounts of energy, a process ...

Nuclear Transmutation

Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with ...

Biological Effects of Radiation

All radioactive nuclides emit high-energy particles or electromagnetic waves. When this radiation encounters living cells, it can cause heating, break ...

Research and communicate the uses, advantages, and disadvantages of nuclear reactions in current technologies.

IPC.8.C

What is Climate?

Climate refers to the prevailing weather conditions in a specific area over an extended period. As the saying goes, &#8220;Climate is what you expect. ...

Global Climate Change

Throughout its ~4.5 billion year history, the Earth has experienced periods of warming and cooling. However, the current drastic increase in global ...

Climate Change

The certainty of climate change remains a public controversy despite the consensus among approximately 97% of active climate researchers, who not only ...

Sustainable Development

As the human population continues to grow and use resources, we must be mindful of our planet&rsquo;s natural limits. Sustainable development provides a ...

Construct and communicate an evidence-based explanation of the environmental impact of the end-products of chemical reactions such as those that may result in degradation of water, soil, air quality, and global climate change.

IPC.8.D

Science concepts. The student knows that changes in matter affect everyday life. The student is expected to:

Stoichiometry, Rates, and Equilibrium

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