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

Las reacciones químicas implican transformaciones químicas de una o más sustancias en diferentes materiales. Una reacción se representa convencionalmente mediante una ecuación química, que utiliza fórmulas químicas para representar átomos, moléculas o compuestos involucrados. Las sustancias presentes al inicio de una reacción y que se consumen durante el proceso se denominan reactivos.Los reactivos se especifican en el lado izquierdo de la ecuación. Las sustancias que se forman durante la reacción se denominan productos y se indican en el lado derecho de la ecuación. Una flecha que separa los reactivos y los productos muestra la dirección de la reacción.Los diferentes estados de la materia se representan mediante abreviaturas entre paréntesis. Una reacción química cumple la ley de conservación de la masa, donde se conservan las masas totales de todos los elementos participantes. Por lo tanto, el número acumulado de átomos de cada elemento coincidirá tanto en los reactivos como en los productos.Las ecuaciones químicas se equilibran utilizando coeficientes numéricos para reflejar el número real de átomos involucrados en la reacción. Es importante cambiar solo los coeficientes numéricos y no los subíndices numéricos que definen la identidad de un compuesto mientras se equilibra cualquier ecuación química. Las directrices generales ayudan a ilustrar y ajustar una ecuación química de manera eficiente.Por ejemplo, la combustión del ácido benzoico líquido, que forma dióxido de carbono gaseoso y agua, se representa inicialmente mediante una ecuación química esquelética. A continuación, los átomos se equilibran ajustando primero los de los compuestos seguidos de los átomos de los elementos libres. La inclusión de los coeficientes siete y tres antes de las fórmulas para el dióxido de carbono y el agua equilibra los átomos de carbono e hidrógeno.Un coeficiente fraccionario de quince por dos ajusta los átomos de oxígeno. Los coeficientes fraccionarios se convierten a números enteros multiplicando la ecuación completa por el denominador. El número colectivo de átomos de cada elemento es igual en ambos lados en una ecuación balanceada.En ecuaciones químicas que representan reacciones que involucran compuestos iónicos, los cationes se equilibran primero, seguidos por los aniones. Los iones poliatómicos siempre se equilibran como una unidad. Por ejemplo, el sulfato de aluminio acuoso reacciona con el hidróxido de calcio acuoso formando hidróxido de aluminio sólido y sulfato de calcio sólido.Usando una ecuación esquelética, los cationes de aluminio y calcio se equilibran, seguidos por los aniones de los iones de hidróxido poliatómico y sulfato. Por último, los coeficientes se ajustan para obtener una ecuación equilibrada general.

ecuaciones químicas

Las ecuaciones químicas representan las identidades y las cantidades relativas de sustancias implicadas en una reacción química. Las sustancias que están en reacción se denominan reactantes y sus fórmulas se colocan en el lado izquierdo de la ecuación. Las sustancias generadas por la reacción se denominan productos y sus fórmulas se colocan en el lado derecho de la ecuación. Los signos más (+) separan las formulas del reactivo individual y del producto, y una flecha (→) separa los lados del reactante y del producto (izquierdo y derecho) de la ecuación. El número relativo de especies de reactantes y productos se representa mediante coeficientes numéricos, colocados inmediatamente a la izquierda de cada fórmula. Normalmente no se muestra un coeficiente de 1. Los coeficientes de número entero más pequeños posibles se utilizan comúnmente en una ecuación química, y se interpretan como proporciones. Por ejemplo, el metano y el oxígeno reaccionan para producir dióxido de carbono y agua en una proporción de 1:2:1:2. 
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/1019/1019_Equations-01.png" style="height: 40px;" />
 
 La proporción indica que los coeficientes más pequeños posibles de metano, oxígeno, dióxido de carbono y agua son 1, 2, 1 y 2, respectivamente. Los coeficientes se pueden interpretar con respecto a cualquier unidad de cantidad (número), y por lo tanto esta ecuación puede leerse correctamente de muchas maneras, incluyendo:
 
 i. Una molécula de metano y dos moléculas de oxígeno reaccionan para producir una molécula de dióxido de carbono y dos moléculas de agua.
 
 ii. Un mol de moléculas de metano y 2 moles de moléculas de oxígeno reaccionan para producir 1 mol de moléculas de dióxido de carbono y 2 moles de moléculas de agua. 
 
 Los estados físicos de los reactantes y productos en las ecuaciones químicas se indican frecuentemente con una abreviatura entre paréntesis después de las fórmulas. Las abreviaturas estándar incluyen ‘s’ para sólidos, ‘l’ para líquidos, ‘g’ para gases y ‘ac’ para sustancias disueltas en agua.
 
 <h4>Balanceo de ecuaciones</h4>
 
 En una ecuación balanceada, el número de átomos para cada elemento implicado en la reacción es el mismo en el lado de los reactantes y en el del producto, satisfaciendo así la ley de conservación de la materia. Una ecuación equilibrada puede confirmarse agregando los números de átomos a ambos lados de la flecha y comparando estas sumas para asegurar que sean iguales. Observe que el número de átomos de un elemento determinado se calcula multiplicando el coeficiente de cualquier fórmula que contenga ese elemento por el subíndice del elemento en la fórmula. Si un elemento aparece en más de una fórmula en un lado dado de la ecuación, el número de átomos representados en cada uno debe ser calculado y luego sumado.
 
 Para equilibrar la ecuación, los coeficientes de la ecuación se pueden cambiar según sea necesario. A veces es conveniente utilizar fracciones en lugar de números enteros como coeficientes intermedios en el proceso de equilibrar una ecuación química. Cuando se logra el equilibrio, todos los coeficientes de la ecuación pueden multiplicarse por un número entero para convertir los coeficientes fraccionarios en enteros sin perturbar el balance atómico. 
 
 Por ejemplo, la reacción del etano (C2H6) con el oxígeno produce agua y dióxido de carbono, que puede representarse mediante la siguiente ecuación no balanceada:
 
 <img alt="Eq2" src="https://www.jovecore.com/CDNSource/lessons/1019/1019_Equations-02.png" style="height: 40px;" />
 
 La ecuación no balanceada contiene: 
 
 <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;">Átomos</td>
 <td style="color: black; border: 1px solid black; text-align: center;">Reactante</td>
 <td style="color: black; border: 1px solid black; text-align: center;">Producto</td>
 <td style="color: black; border: 1px solid black; text-align: center;">¿Balanceado? </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;">No </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;">No </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;">No</td>
 </tr>
 </tbody>
 </table>
 
 Para balancear el número de átomos de carbono y de hidrógeno, multiplique CO2 por el coeficiente 2 y multiplique H2O por el coeficiente 3, respectivamente. Esto cambia el número total de átomos de oxígeno en el producto a 7. Para balancear el número de átomos de oxígeno, multiplique el oxígeno por el coeficiente fraccional 7/2. Este balanceo inicial de los átomos de carbono, hidrógeno y oxígeno al cambiar los coeficientes de reactivos y productos, proporciona la ecuación provisionalmente balanceada: 
 
 <img alt="Eq3" src="https://www.jovecore.com/CDNSource/lessons/1019/1019_Equations-03.png" style="height: 40px;" />
 
 Una ecuación convencional balanceada sólo con coeficientes de números enteros se obtiene multiplicando cada coeficiente por 2 para generar la ecuación:
 
 <img alt="Eq4" src="https://www.jovecore.com/CDNSource/lessons/1019/1019_Equations-04.png" style="height: 40px;" />
 
 Este texto ha sido adaptado de <a href="https://openstax.org/books/chemistry-2e/pages/4-1-writing-and-balancing-chemical-equations">Openstax, Química 2e, Sección 4.1: Escritura y Balanceo de Ecuaciones Químicas</a>.

Ecuaciones Químicas

Las ecuaciones químicas representan las identidades y cantidades relativas de las sustancias involucradas en una reacción química. Las sustancias que se someten a la reacción son ...

Education

Educación

JoVE Core

Química

Molecules, Compounds, and Chemical Equations

Moléculas, compuestos y ecuaciones químicas

molecules-compounds-and-chemical-equations

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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

Finding Empirical and Molecular Formulas

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 Química da vida a los conceptos de química general mediante lecciones de vídeo basadas en animaciones, concisas y fáciles de entender. Además, en los vídeos de científicos en acción, se muestran experimentos de investigación clásicos y originales realizados en laboratorios de todo el mundo.

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

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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

Scientific Laws

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Classifying Matter by State

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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

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

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 Stability

Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10&#8722;15 meters, a nucleus is ...

Nuclear Binding Energy

The difference between the calculated and experimentally measured masses is known as the mass defect of the atom. In the case of helium-4, the mass defect ...

Radioactive Decay and Radiometric Dating

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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

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Nuclear Fusion

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Use models to compare nuclear reactions including alpha decay, beta decay and gamma decay; nuclear fusion and nuclear fission.

PS.Chm.1.2

Atomic Orbitals

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The Pauli Exclusion Principle

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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 ...

The Aufbau Principle and Hund's Rule

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Electron Configuration of Multielectron Atoms

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the ...

Use models to explain how electrons are distributed in atoms.

PS.Chm.1.3

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Atomic Mass

Atoms &mdash; and the protons, neutrons, and electrons that compose them &mdash; are extremely small. For example, a carbon atom weighs less than 2 ...

Molar Mass

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Use the Periodic Table as a model to predict the relative properties of elements based on the pattern of valence electrons in the outermost energy levels of atoms.

PS.Chm.2.1

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

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Ionization Energy

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Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



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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.

PS.Chm.2.2

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Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

Ionic Bonding and Electron Transfer

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The Born-Haber Cycle

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Trends in Lattice Energy: Ion Size and Charge

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Covalent Bonding and Lewis Structures

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Electronegativity

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Electronegativity values of ...

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

PS.Chm.3.1

Analyze the structure of atoms and isotopes.

Reading Chemical Equations and Balancing Them

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