Name: reading chemical equations and balancing them
Uploaded: 2020-09-03T13:38:26.000Z
Duration: 3 min 10 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.4.2

Chemical Equations

化学反应是一种或多种 物质变成不同的物质的化学转化。一个反应通常 用化学方程式来表示，它利用 化学式来表示所涉及的原子、分子 或化合物。反应开始时存在 并在反应过程中被消耗的物质称为反应物。反应物指定在方程式的左边。反应过程中形成的物质称为产物，并在方程式的右边显示。将反应物和产物分开的箭头 表示反应的方向。物质的不同状态 用括号中的缩写来描述。化学反应遵循质量守恒定律，即所有参与反应的元素的总质量 是守恒的。因此，每种元素的累积原子数 在反应物和产物中都是匹配的。化学方程式是用数值系数来平衡的，以反映参与反应的原子的实际数量。重要的是，在平衡任何化学方程式时 只改变数值系数，而不改变定义化合物 同一性的数值下标。一般的指导方针有助于有效地说明和调整 一个化学方程式。例如，液体苯甲酸的燃烧，形成 气态二氧化碳和水，最初是 用骨架化学方程式来表示的。接下来首先调整化合物中的原子 然后调整自由元素的原子使原子达到平衡。在二氧化碳和水的分子式前面 加上系数 7 和 3 平衡了碳原子和氢原子。二分之十五的分数系数 调整了氧原子。通过将整个方程式乘以分母，分数系数被转换成整数。平衡方程式中每种元素的原子 总数在两边是相等的。在有离子化合物参与反应的 化学方程式中，应首先 平衡阳离子，其次是阴离子。多原子离子总是作为一个整体来平衡的。例如，硫酸铝溶液 与氢氧化钙溶液反应 生成固体氢氧化铝和固体硫酸钙。利用骨架方程式，铝和钙的阳离子 达到平衡，其次是多原子氢氧化物和硫酸根离子的 阴离子的平衡。最后，对系数进行调整，得到一个整体平衡方程式。

化学方程式

化学方程式表示化学反应中涉及的物质的身份和相对数量。发生反应的物质称为反应物，其分子式位于方程式的左侧。反应产生的物质称为产物，其公式位于等式的右侧。加号（+）分隔了各个反应物和产物的化学式，箭头（＆rarr;）分隔了方程式中的反应物和产物（左右）。反应物和产物种类的相对数量由数字系数表示，该系数紧接在每个公式的左侧。通常通常不显示系数1。最小的整数系数通常在化学方程式中使用，它们被解释为比率。例如，甲烷和氧气反应生成1：2：1：2的二氧化碳和水。
 
 <img alt =“ Eq1” src =“ https://www.jove.com/files/core/CDNSource/lessons/1019/1019_Equations-01.png” style =“height: 40px;“ /> 
 
 该比率表明甲烷，氧气，二氧化碳和水的最小可能系数分别为1、2、1和2。可以针对任何数量（数量）单位来解释系数，因此可以通过多种方式正确读取此方程式，包括：
 
 i。一个甲烷分子和两个氧分子反应生成一个二氧化碳分子和两个水分子。
 
 ii。一摩尔的甲烷分子和2摩尔的氧分子反应生成1摩尔的二氧化碳分子和2摩尔的水分子。
 
 在化学方程式中，反应物和产物的物理状态经常用分子式后的括号来表示。标准缩写包括“ s ”＆rsquo;对于固体，＆lt; l ＆rsquo;对于液体，“ g ＆rsquo;气体和 aq ＆rsquo;溶解在水中的物质。
 
 <h4>平衡方程</ h4>
 
 在平衡方程中，反应中涉及的每个元素的原子数在反应物和产物侧均相同，从而满足物质守恒定律。可以通过在箭头的两边加上原子数并比较这些和以确保它们相等来确认平衡方程。注意，给定元素的原子数是通过将包含该元素的任何公式的系数乘以公式中的元素下标来计算的。如果某个元素在方程式的给定一侧出现在多个公式中，则必须计算每个元素中表示的原子数，然后将它们加在一起。
 
 为了平衡方程式，可以根据需要更改方程式的系数。在平衡化学方程式的过程中，有时方便使用分数而不是整数作为中间系数。当达到平衡时，所有等式的系数都可以乘以整数，以将分数系数转换为整数，而不会破坏原子平衡。
 
 例如，乙烷（C 2 H 6 ）与氧气反应生成水和二氧化碳，可用以下不平衡方程表示：</ >
 
 <img alt="Eq2" src="https://www.jove.com/files/core/CDNSource/lessons/1019/1019_Equations-02.png" style="height: 40px;" />
 
 不平衡方程包含： 
 
 <table style="margin-left: auto; margin-right: auto;">
 <tbody style="border: 1px solid black;">
 <tr>
 <td style="color: black; border: 1px solid black; text-align: center;">原子</td>
 <td style="color: black; border: 1px solid black; text-align: center;">反应物</td>
 <td style="color: black; border: 1px solid black; text-align: center;">生成物</td>
 <td style="color: black; border: 1px solid black; text-align: center;">平衡？</td>
 </tr>
 <tr>
 <td style="color: black; border: 1px solid black; text-align: center;">C</td>
 <td style="color: black; border: 1px solid black; text-align: center;">2</td>
 <td style="color: black; border: 1px solid black; text-align: center;">1</td>
 <td style="color: black; border: 1px solid black; text-align: center;">否</td>
 </tr>
 <tr>
 <td style="color: black; border: 1px solid black; text-align: center;">H</td>
 <td style="color: black; border: 1px solid black; text-align: center;">6</td>
 <td style="color: black; border: 1px solid black; text-align: center;">2</td>
 <td style="color: black; border: 1px solid black; text-align: center;">否</td>
 </tr>
 <tr>
 <td style="color: black; border: 1px solid black; text-align: center;">O</td>
 <td style="color: black; border: 1px solid black; text-align: center;">2</td>
 <td style="color: black; border: 1px solid black; text-align: center;">3</td>
 <td style="color: black; border: 1px solid black; text-align: center;">否</td>
 </tr>
 </tbody>
 </table>
 
 要平衡碳原子和氢原子的数量，请分别将CO 2 乘以系数2，将H 2 O乘以系数3。这会将产品上的氧原子总数更改为7。要平衡氧原子数目，请用氧乘以分数系数7/2。通过更改反应物和产物的系数，碳，氢和氧原子的这种初始平衡给出了暂时平衡的方程式：
 
 <img alt="Eq3" src="https://www.jove.com/files/core/CDNSource/lessons/1019/1019_Equations-03.png" style="height: 40px;" />
 
 通过将每个系数乘以2来生成常规的仅具有整数系数的平衡方程，以生成方程：
 
 <img alt="Eq4" src="https://www.jove.com/files/core/CDNSource/lessons/1019/1019_Equations-04.png" style="height: 40px;" />
 
 本文改编自<a href="https://openstax.org/books/chemistry-2e/pages/4-1-writing-and-balancing-chemical-equations"> Openstax，化学2e，第4.1节：编写和平衡化学方程式</a>。

化学方程式表示参与化学反应的物质的种类及其相对数量。发生反应的物质是……

Education

教育

JoVE Core

化学

Molecules, Compounds, and Chemical Equations

分子、化合物与化学方程式

molecules-compounds-and-chemical-equations

KEY TERMS AND CONCEPTS

关键术语与概念

reading chemical equations and balancing them

Chemical equations show the identities and relative amounts of substances in a chemical reaction. The substances that react are called reactants, and their formulas are written on the left side of the equation. The substances formed are called products, and their formulas are written on the right side. A plus sign (+) separates formulas on the same side, and an arrow (→) shows the change from reactants to products.

The numbers in a chemical equation are shown with coefficients. A coefficient is the number written in front of a formula. A coefficient of 1 is usually not written. The smallest whole-number coefficients are commonly used, and they work as ratios. For example, methane and oxygen react to form carbon dioxide and water in a 1:2:1:2 ratio.

That ratio can be read in more than one way. It can mean 1 methane molecule and 2 oxygen molecules make 1 carbon dioxide molecule and 2 water molecules. It can also mean 1 mole of methane molecules and 2 moles of oxygen molecules make 1 mole of carbon dioxide molecules and 2 moles of water molecules. Chemical equations may also include physical states after the formulas. Common state labels are s for solid, l for liquid, g for gas, and aq for substances dissolved in water.

A balanced chemical equation has the same number of atoms for each element on both sides. This follows the law of conservation of matter. To check balance, count the atoms on the reactant side and the product side and compare the totals. To find the number of atoms in a formula, multiply the coefficient by the subscript. If an element appears in more than one formula on one side, add all of those atoms together.

Balancing a chemical equation means changing coefficients, not the formulas themselves. Fractions can be used as temporary coefficients during balancing. For the reaction of ethane with oxygen, carbon and hydrogen are balanced first by placing 2 in front of carbon dioxide and 3 in front of water. That leaves 7 oxygen atoms on the product side, so oxygen gets a fractional coefficient of 7/2. The final equation is then multiplied by 2 to turn all coefficients into whole numbers without changing the balance.

Reading Chemical Equations and Balancing Them

reading-chemical-equations-and-balancing-them

molecules and compounds

Atomic Elements, Molecules, and Bonds

Matter is made of elements, and elements are built from atoms. An atom is the smallest unit of an element that still keeps that element’s properties. A silver coin, for example, is made of silver atoms. Each atom keeps the unique properties of silver. Elements are pure substances made of identical atoms. They cannot be broken down into simpler substances by chemical changes. Most elements are atomic elements, which use single atoms as their basic unit. Carbon and sodium are examples of atomic...

molecular models

Molecular Model Types in Chemistry

Molecular models help chemists and students visualize the structures and shapes of atoms and molecules. They represent the molecular architecture of chemical compounds in a way that is easier to study than formulas alone. Skeletal models are simple two-dimensional drawings of compounds. They show the molecular framework, or the bonds, without drawing every atom. In this model, many carbon and hydrogen atoms are not shown directly. Their positions are implied by the ends and junctions of the...

organic compounds

Organic Molecules in Everyday Chemistry

Organic molecules are carbon-based compounds found in living things and in many everyday products. Most organic compounds have carbon as the main element, bonded to hydrogen and other carbon atoms. Some carbon-containing substances, such as carbonates, cyanides, and simple oxides like CO and CO2, are not classified as organic. Carbon can form up to four strong bonds, which helps explain why organic compounds can make chains and rings of many sizes and shapes. These molecules appear in...

formula mass and mole concepts of compounds

formula-mass-and-mole-concepts-of-compounds

Chemical Formula Mass and Percent Composition

Chemical formula mass and percent composition help describe the makeup of compounds. A chemical formula shows which atoms are present and how many of each atom appear in a substance. For covalent compounds, the formula shows the atoms in one molecule. That is why formula mass can also be called molecular mass. Chloroform, CHCl3, is one example. Its formula shows one carbon atom, one hydrogen atom, and three chlorine atoms. The molecular mass is the sum of their average atomic masses. Ionic...

experimental determination of chemical formula

experimental-determination-of-chemical-formula

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Chemical formulas show the elemental makeup of a compound. When a formula is unknown, scientists often start by measuring the masses of the elements in the sample. Those mass data are then used to find the simplest whole-number ratio of atoms, which gives the empirical formula. To get from mass to atom ratio, the masses of the elements are first converted to moles using molar masses. Chemical formulas describe numbers of atoms, not masses, so this step is necessary. In one example, 1.71 grams...

chemical equations

Chemical equations show the identities and relative amounts of substances in a chemical reaction. The substances that react are called reactants, and their formulas are written on the left side of the equation. The substances formed are called products, and their formulas are written on the right side. A plus sign (+) separates formulas on the same side, and an arrow (→) shows the change from reactants to products. The numbers in a chemical equation are shown with coefficients. A coefficient...

key terms and concepts

Learn how to read chemical equations, identify reactants and products, use coefficients and state symbols, and balance equations with whole-number ratios.

Reading Chemical Equations and Balancing Them | JoVE K12

chemistry

JoVE Core 化学通过简单明了且通俗易懂的动画视频课程，将普通化学概念带入到现实生活当中。此外，在科学家行动视频中，我们演示了在实验室中进行的经典和原始研究实验。

Physical Science

PS.PSc.2.3

Pennsylvania State Academic Standards

Chemical Reactions

3.2.9-12.C

3.2.9-12.G

Louisiana Student Standards for Science

High School

Matter And Its Interactions

HS-PS1-2

HS-PS1-7

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Study Of Matter

Reactions of matter

Interactions Of Matter

Chemical reactions

Stoichiometry

Tennessee Academic Standards

Matter and Its Interactions

CHEM1.PS1.2

CHEM1.PS1.3

Virginia  Standards of Learning

HIgh School

CH.3

CH.3.a

CH.3.b

CH.3.c

PS.3

PS.3.d

Minnesota Academic Standards in Science

2.2.1 9C.1.2.1.2

Arizona Science Standards

HS+C.P1

HS+C.P1U1.5

HS+C.P1U1.7

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

New Jersey Student Learning Standards for Science

Texas Essential Knowledge and Skills

CHEM.7

CHEM.7.B

CHEM.9

CHEM.9.A

Alabama Course of Study Science

9-12.PS.3.5.d

Next Generation Science Standards

Florida Department of Education

SC.912.P.8

SC.912.P.8.9

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

South Carolina College and Career Ready Science Standards

C-PS1-2

C-PS1-7

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-4.

HS-PS1-7.

HS-PS1-12.

Georgia Standards of Excellence

SPS3.

Chemical Reaction

SC3.

balancing-chemical-equations-and-reaction-outcomes

Balancing Chemical Equations and Reaction Outcomes

Scientific Laws and Theories

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Classifying Matter by Composition

Matter: Pure Substances and Mixtures
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The Atomic Theory of Matter

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Subatomic Particles

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Elements: Chemical Symbols and Isotopes

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Use models to explain how the scientific understanding of atomic structure has evolved.

PS.Chm.1.1

Radioactivity and Nuclear Equations

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Types of Radioactivity

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Nuclear Binding Energy

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Radioactive Decay and Radiometric Dating

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Nuclear Fission

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The Energies of Atomic Orbitals

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The Aufbau Principle and Hund's Rule

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electron-configuration-of-multielectron-atoms

Electron Configuration of Multielectron Atoms

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Use models to explain how electrons are distributed in atoms.

PS.Chm.1.3

Periodic Classification of the Elements

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The Periodic Table

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Atomic Mass

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Molar Mass

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Electron Affinity

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Construct an explanation to infer the atomic size, reactivity, electronegativity, and ionization energy of an element based on its position in the Periodic Table.

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Bond Polarity

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Analyze and interpret data to explain the mechanisms and properties of the two main types of intramolecular (ionic and covalent) bonds.

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Analyze the structure of atoms and isotopes.

Reading Chemical Equations and Balancing Them

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