Name: building and breaking in chemical reactions
Uploaded: 2020-09-03T13:38:26.000Z
Duration: 2 min 17 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.6.1

Synthesis and Decomposition Reactions

Generally, in a chemical reaction, molecules interact by breaking one set of bonds and forming a new set of bonds.&nbsp;

A redox, or oxidation&ndash;reduction, reaction is a type of chemical reaction involving the partial or complete transfer of electrons. In such reactions, one reactant is oxidized and the other is reduced, with an observable change in their oxidation states.&nbsp;

The oxidized element, which has lost electrons, undergoes an increase in oxidation state. The reduced element, which has gained electrons, undergoes a decrease in oxidation state.

Among the most common redox reactions are synthesis and decomposition reactions. The synthesis of proteins from different amino acids and the digestion of proteins into amino acids are important examples.

Synthesis, or combination, reactions involve the formation of bonds between reactants to create a single product. The reactants may include only elements, elements and compounds, or only compounds.&nbsp;

Examples are the combination of elemental hydrogen and oxygen to create water, the addition of carbon monoxide to elemental oxygen to form carbon dioxide, and the combination of calcium oxide and water to form calcium hydroxide.

Notice that in al

synthesis and decomposition reactions

Synthesis and decomposition are two types of redox reactions. Synthesis means to make something, whereas decomposition means to break something. The reactions are accompanied by chemical and energy changes.&nbsp;

<h4>Synthesis Reactions</h4>

Synthesis reactions are also called combination reactions. It is a reaction in which two or more substances combine to form a complex substance. Synthesis reactions are generally represented as: A + B &rarr; AB or A + B &rarr; C. The formation of nitrogen dioxide is a synthesis reaction: 2 NO (g) + O2 (g) &rarr; 2 NO2 (g).

In synthesis reactions, the reactants could be all elements (1), or a combination of an element and a compound (2), or all compounds (3).

1) C (s) + O2 (g) &rarr; CO2 (g) &nbsp; &nbsp; 
2) 2 CO (g) + O2 (g) &rarr; 2 CO2 (g)&nbsp; 
3) 2 CaO (s) + 2 H2O (l) &rarr; 2 Ca(OH)2 (s)

A combination reaction between a metal and a nonmetal always produces an ionic solid. For example, the formation of sodium chloride or table salt from sodium and chlorine is a combination reaction: 2 Na (s) + Cl2 (g) &rarr; 2 NaCl (s).

A synthesis reaction is generally accompanied by the release of energy. In the above example of sodium chloride, 787 kJ of heat energy is released.&nbsp;

<h4>Decomposition Reactions</h4>

Oxygen was first discovered by the scientist Joseph Priestley, in 1774, by heating mercury oxide with a burning glass. The reaction was a result of decomposition. Priestley had broken down mercury(II) oxide with heat into its elements.&nbsp; 
The reaction is represented as: 2 HgO (s) &rarr; 2 Hg (l) + O2 (g)

Decomposition reactions involve breaking down a more complex substance into two or more smaller substances. This reaction is often represented as: AB &rarr; A + B or C &rarr; A + B. Decomposition reactions occur everywhere. For instance, the digestion of proteins, fats, and carbohydrates in our food is an important decomposition reaction. Another example is the decomposition of sodium azide into nitrogen gas.&nbsp;

The reaction is represented as: 2 NaN3 (s) &rarr; 2 Na (s) + 3 N2 (g)

In the above reaction, although the coefficient 2 indicates two molecules of sodium azide being decomposed, there is only one reactant. It is, therefore, a decomposition reaction. Similar to the synthesis reaction, in a decomposition reaction, the products formed could be all elements (1), or a combination of elements and compounds (2), or all compounds (3).

1)&nbsp;&nbsp; &nbsp;2 Al2O3 (s) &rarr; 4 Al (s) + 3 O2 (g) 
2)&nbsp;&nbsp; &nbsp;2 KClO3 (s) &rarr; 2 KCl (s) + 3 O2 (g) 
3)&nbsp;&nbsp; &nbsp;NH4Cl (s) &rarr; NH3 (g) + HCl (g)

Synthesis and decomposition are two types of redox reactions. Synthesis means to make something, whereas decomposition means to break something. The ...

Education

JoVE Core

Chemical Quantities and Aqueous Reactions

chemical-quantities-and-aqueous-reactions

KEY TERMS AND CONCEPTS

building and breaking in chemical reactions

Synthesis and decomposition are two redox reactions that show how substances can be built up or broken down. Synthesis means to make something, while decomposition means to break something apart. These reactions also involve chemical changes and energy changes.

Synthesis reactions are also called combination reactions. In a synthesis reaction, two or more substances join to form one more complex substance. They are often written as A + B → AB or A + B → C. One example is the formation of nitrogen dioxide: 2 NO (g) + O2 (g) → 2 NO2 (g).

The reactants in a synthesis reaction can take several forms. They may be all elements, an element and a compound, or all compounds. Examples include C (s) + O2 (g) → CO2 (g), 2 CO (g) + O2 (g) → 2 CO2 (g), and 2 CaO (s) + 2 H2O (l) → 2 Ca(OH)2 (s). When a metal reacts with a nonmetal, the product is always an ionic solid. Sodium chloride is a clear example: 2 Na (s) + Cl2 (g) → 2 NaCl (s).

Synthesis reactions are generally accompanied by the release of energy. In the sodium chloride example, 787 kJ of heat energy is released. Decomposition reactions are the opposite pattern. They break one complex substance into two or more smaller substances. They are often written as AB → A + B or C → A + B.

A famous decomposition reaction helped oxygen gas be discovered by Joseph Priestley in 1774. He heated mercury oxide with a burning glass and broke mercury(II) oxide down into its elements: 2 HgO (s) → 2 Hg (l) + O2 (g). Decomposition reactions also occur in everyday life. The digestion of proteins, fats, and carbohydrates is one example. Another is the breakdown of sodium azide into nitrogen gas: 2 NaN3 (s) → 2 Na (s) + 3 N2 (g).

Even when the coefficient shows more than one molecule, a reaction can still be a decomposition reaction if there is only one reactant. In the sodium azide example, there is one reactant substance that breaks apart. The products of decomposition can be all elements, a mix of elements and compounds, or all compounds. Examples include 2 Al2O3 (s) → 4 Al (s) + 3 O2 (g), 2 KClO3 (s) → 2 KCl (s) + 3 O2 (g), and NH4Cl (s) → NH3 (g) + HCl (g).

Building and Breaking in Chemical Reactions

building-and-breaking-in-chemical-reactions

reaction stoichiometry

Using Balanced Equations to Predict Amounts

Balanced chemical equations show how much of each substance reacts and forms in a chemical change. The formulas identify the reactants and products, which helps classify the reaction. The coefficients show the relative numbers of each substance, which lets chemists measure the relationships between amounts consumed and produced. These quantitative relationships are called stoichiometry. The word comes from the Greek words stoicheion, meaning element, and metron, meaning measure. Stoichiometry...

limiting reactant

Limiting Reactant in Water Formation

Limiting reactants control how much product forms in a chemical reaction. In a balanced equation, the listed amounts of reactants and products are called stoichiometric amounts. In real reactions, the reactants are not always present in those exact proportions. The limiting reactant is the reactant that gets used up first. Once it is gone, the reaction stops making more product. The other reactant is called the excess reactant. Chemists often use extra amounts of one reactant to make sure the...

reaction yield

Calculating Percent Yield in Reactions

Percent yield shows how much product a chemical reaction actually makes compared with how much it should make. The expected amount is called the theoretical yield. It comes from the balanced chemical equation and the stoichiometry, or mole ratios, in that equation. The theoretical yield assumes that the limiting reactant is completely converted into the desired product. The product collected after a reaction is the actual yield. In many cases, the actual yield is lower than the theoretical...

general properties of solutions

Solvents, Solutes, and Solution Types

Solutions are common mixtures found in everyday life. Ocean water, air, and gasoline are all examples of solutions. These mixtures contain two or more types of atoms or molecules in varying amounts. A solution is a homogeneous mixture, which means its composition is uniform throughout. This is different from a heterogeneous mixture, which has a non-uniform composition. In a homogeneous mixture, the components are evenly spread out and thoroughly mixed. Every solution has a solvent and a...

solution concentration and dilution

Molarity and Dilution in Solutions

Molarity and dilution are key ideas for describing solution concentration. Concentration means the relative amount of one component in a solution. In many solutions, one component is present in much larger amount. That component is the solvent, which acts as the medium that holds the other parts dissolved or dispersed. Water is a very common solvent, so aqueous solutions are common on Earth. A solute is the component present at a much lower concentration than the solvent. Chemists often...

electrolyte and nonelectrolyte solutions

Conductivity in Electrolyte Solutions

Electrolyte solutions conduct electricity because they contain mobile ions. The amount of current depends on how many ions are present in the aqueous solution. A solution with more dissolved ions conducts better, while a solution with few or no ions conducts poorly. Strong electrolytes dissociate completely in water. This complete dissociation is shown with a single forward arrow. Water-soluble ionic compounds such as sodium chloride split into sodium cations and chloride anions in solution.

solubility of ionic compounds

Solubility Rules for Ionic Salts

Solubility rules help predict whether ionic salts will dissolve in water. Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a set temperature and pressure. It is often measured in molarity, or moles per liter (mol/L). A compound is soluble if it dissolves in water. When a soluble salt dissolves, its ions separate and spread evenly through the solution. This physical change is called dissociation. Potassium chloride, KCl, is a simple example. Water...

chemical reactions in aqueous solutions

Aqueous Reactions and Ionic Equations

Aqueous reactions are chemical reactions that take place in water. Water is a good solvent, so it can dissolve many substances. Because of that, many chemical reactions happen in aqueous solution. In high school chemistry, these reactions are often grouped into three common patterns: precipitation, acid-base, and oxidation-reduction. A precipitation reaction happens when ions in two aqueous ionic compounds exchange partners and form an insoluble salt, called a precipitate. In an acid-base...

precipitation reactions

Predicting Precipitation in Aqueous Reactions

Precipitation reactions happen when two aqueous solutions of soluble salts are mixed and an insoluble ionic compound forms. That solid is called a precipitate. The ions in solution exchange partners, so these reactions are also called double displacement, double replacement, exchange, or metathesis reactions. These reactions are useful in chemistry for identifying metal ions in a compound. They also support gravimetric methods, which measure composition by the mass of a substance. Whether a...

oxidation-reduction reactions

Redox Reactions and Oxidation Numbers

Redox reactions are chemical changes in which electrons move between reactants, and oxidation numbers help track that change. The term oxidation once referred only to reactions with molecular oxygen, but it now covers a wider reaction class called oxidation-reduction, or redox, reactions. Some redox reactions form ionic products. A simple example is the reaction between sodium and chlorine that produces sodium chloride. To follow what happens to each reactant, chemists often write...

oxidation numbers

Assigning Oxidation States in Redox Reactions

Oxidation states help track electron transfer in redox reactions. An oxidation number, also called an oxidation state, is a hypothetical number that shows the effective charge of an atom or element. Chemists assign it by using a set of rules. In an ionic compound, oxidation numbers are based on how many electrons move between reacting species. For example, when calcium chloride forms, calcium loses two valence electrons and the two chlorine atoms each gain one electron. In CaCl2, calcium has...

acids, bases and neutralization reactions

How Acids and Bases Form Ions

Acids and bases form ions in water through acid-base reactions. These reactions move a hydrogen ion, H+, from one chemical species to another. They matter in many natural and technological processes, from chemistry inside cells and in lakes and oceans to the large-scale production of fertilizers, pharmaceuticals, and other useful substances. In water, an acid is a substance that produces hydrogen ions. This is the Arrhenius definition of an acid. The H+ ion is also called a proton. In...

Synthesis and decomposition are two redox reactions that show how substances can be built up or broken down. Synthesis means to make something, while decomposition means to break something apart. These reactions also involve chemical changes and energy changes. Synthesis reactions are also called combination reactions. In a synthesis reaction, two or more substances join to form one more complex substance. They are often written as A + B → AB or A + B → C. One example is the formation of...

key terms and concepts

Learn how synthesis reactions build new compounds and decomposition reactions break substances apart, with clear examples like sodium chloride, mercury oxide, and sodium azide.

Building and Breaking in Chemical Reactions | JoVE K12

chemistry

JoVE Core Chemistry brings general chemistry concepts to life using concise and easy-to-understand animated video lessons. Plus, in the scientist-in-action videos, we demonstrate classical and original research experiments performed in today's laboratories worldwide.

Physical Science

PS.PSc.2.4

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

Interactions Of Matter

Chemical reactions

Tennessee Academic Standards

Matter and Its Interactions

CHEM1.PS1.4

Arizona Science Standards

HS+C.P1

HS+C.P1U1.5

Alabama Course of Study Science

Matter and Its Interactions: Energy

9-12.C.3.3

9-12.PS.3.5.d

Florida Department of Education

SC.912.P.8

SC.912.P.8.8

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-4.

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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PS.Chm.1.1

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Nuclear Power

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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

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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

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electron-configuration-of-multielectron-atoms

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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

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Molar Mass

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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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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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lewis-structures-of-molecular-compounds-and-polyatomic-ions

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Resonance

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Formal Charges

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Exceptions to the Octet Rule

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	...

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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.

PS.Chm.3.1

Analyze the structure of atoms and isotopes.

Building and Breaking in Chemical Reactions

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