Is a type of chemical reaction in which two or more simple substances combine to form a more complex product?

chemical synthesis, the construction of complex chemical compounds from simpler ones. It is the process by which many substances important to daily life are obtained. It is applied to all types of chemical compounds, but most syntheses are of organic molecules.

Chemists synthesize chemical compounds that occur in nature in order to gain a better understanding of their structures. Synthesis also enables chemists to produce compounds that do not form naturally for research purposes. In industry, synthesis is used to make products in large quantity.

Chemical compounds are made up of atoms of different elements, joined together by chemical bonds. A chemical synthesis usually involves the breaking of existing bonds and the formation of new ones. Synthesis of a complex molecule may involve a considerable number of individual reactions leading in sequence from available starting materials to the desired end product. Each step usually involves reaction at only one chemical bond in the molecule.

In planning the route of chemical synthesis, chemists usually visualize the end product and work backward toward increasingly simpler compounds. For many compounds, it is possible to establish alternative synthetic routes. The ones actually used depend on many factors, such as cost and availability of starting materials, the amount of energy needed to make the reaction proceed at a satisfactory rate, and the cost of separating and purifying the end products. Moreover, knowledge of the reaction mechanism and the function of the chemical structure (or behaviour of the functional groups) helps to accurately determine the most-favoured pathway that leads to the desired reaction product.

A goal in planning a chemical synthesis is to find reactions that will affect only one part of the molecule, leaving other parts unchanged. Another goal is to produce high yields of the desired product in as short a time as possible. Often, reactions in a synthesis compete, reducing the yield of a desired product. Competition can also lead to the formation of side products which can be difficult to separate from the main one. In some industrial syntheses, by-product formation can be welcome if the by-products are commercially useful. Diethyl ether, for example, is a by-product of the large-scale synthesis of ethanol (ethyl alcohol) from ethylene. Both the alcohol and ether are valuable and can be separated easily.

The reactions involved in chemical syntheses usually, but not always, involve at least two different substances. Some molecules will change into others solely under the effect of heat, for example, while others react on exposure to radiation (e.g., ultraviolet light) or to electric current. However, where two or more different substances interact, they need to be brought into close proximity with one another. This is usually done by carrying out the syntheses with the elements or compounds in their liquid or gaseous states. Where the reactants are involatile solids, reaction is often carried out in solution.

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The rate of a chemical reaction generally increases with temperature; chemical syntheses are thus often carried out at elevated temperatures. The industrial synthesis of nitric acid from ammonia and oxygen, for instance, is carried out at about 900 °C (1,650 °F). Frequently, heating will increase the rate of a reaction insufficiently or the instability of one or more reactants prevents application. In such cases catalysts—substances that speed up or slow down a reaction—are used. Most industrial processes involve the use of catalysts.

Some substances react so rapidly and violently that only careful control of the conditions will lead to the desired product. When ethylene gas is synthesized to polyethylene, one of the most common plastics, a large amount of heat is released. If this release is not controlled in some way—e.g., by cooling the reactor vessel—the ethylene molecules decompose to carbon and hydrogen.

Many techniques have been developed to separate the products of chemical synthesis. These often involve a phase change. For example, the product of a synthetic reaction may not dissolve in a particular solvent, while the starting materials do. In this case, the product will precipitate out as a solid and can be separated from the mixture by filtration. Alternatively, if both starting materials and products are volatile, it may be possible to separate them by distillation.

Certain chemical syntheses lend themselves readily to the use of automated techniques. Automatic DNA (deoxyribonucleic acid) synthesizers, for example, are widely used to produce specific protein sequences.

Answer

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Hint: To solve this we must know what happens in a synthesis reaction. Recall all the reactions you have learned to find out what happens in a synthesis reaction.A reaction of an acid and a base is known as the neutralization reaction. In a neutralization reaction, acid and base react to form salt and water.

Complete step by step solution: We are asked what happens in a synthesis reaction. Synthesis reaction is also known as direct combination reaction.

The word ‘synthesis’ indicates that in the reaction a product is synthesised or formed.Synthesis reaction is a reaction in which two or more simple substances combine to form a complex product.The reactants of a synthesis reaction can be elements or compounds but the products are always a compound.The general form of a synthesis reaction is as follows:${\text{A}} + {\text{B}} \to {\text{AB}}$An example of synthesis reaction is the reaction of sodium $\left( {{\text{Na}}} \right)$ and chlorine $\left( {{\text{Cl}}} \right)$ in which sodium and chlorine combine to produce sodium chloride $\left( {{\text{NaCl}}} \right)$.Thus, we can conclude that a synthesis reaction is a reaction in which two or more substances combine to form a new compound.

Thus, the correct option is (A) a reaction in which two or more substances combine to form a new compound.

Note: The reaction opposite to synthesis reaction is a decomposition reaction. In a decomposition reaction, one complex reactant breaks down to two or more simple products.A reaction in which two or more compounds combine to form a new compound is known as combination reaction.

Learning Outcomes

Classify a reaction as combination, decomposition, single-replacement, double-replacement, or combustion.
Predict the products and balance a combustion reaction.

Many chemical reactions can be classified as one of five basic types. Having a thorough understanding of these types of reactions will be useful for predicting the products of an unknown reaction. The five basic types of chemical reactions are combination, decomposition, single-replacement, double-replacement, and combustion. Analyzing the reactants and products of a given reaction will allow you to place it into one of these categories. Some reactions will fit into more than one category.

A combination reaction, also known as a synthesis reaction, is a reaction in which two or more substances combine to form a single new substance. Combination reactions can also be called synthesis reactions .The general form of a combination reaction is:

\[\ce{A} + \ce{B} \rightarrow \ce{AB}\]

One combination reaction is two elements combining to form a compound. Solid sodium metal reacts with chlorine gas to product solid sodium chloride.

\[2 \ce{Na} \left( s \right) + \ce{Cl_2} \left( g \right) \rightarrow 2 \ce{NaCl} \left( s \right)\]

Notice that in order to write and balance the equation correctly, it is important to remember the seven elements that exist in nature as diatomic molecules ($\ce{H_2}$, $\ce{N_2}$, $\ce{O_2}$, $\ce{F_2}$, $\ce{Cl_2}$, $\ce{Br_2}$, and $\ce{I_2}$).

One sort of combination reaction that occurs frequently is the reaction of an element with oxygen to form an oxide. Metals and nonmetals both react readily with oxygen under most conditions. Magnesium reacts rapidly and dramatically when ignited, combining with oxygen from the air to produce a fine powder of magnesium oxide.

\[2 \ce{Mg} \left( s \right) + \ce{O_2} \left( g \right) \rightarrow 2 \ce{MgO} \left( s \right)\]

A decomposition reaction is a reaction in which a compound breaks down into two or more simpler substances. The general form of a decomposition reaction is:

\[\ce{AB} \rightarrow \ce{A} + \ce{B}\]

Most decomposition reactions require an input of energy in the form of heat, light, or electricity.

Binary compounds are compounds composed of just two elements. The simplest kind of decomposition reaction is when a binary compound decomposes into its elements. Mercury (II) oxide, a red solid, decomposes when heated to produce mercury and oxygen gas.

\[2 \ce{HgO} \left( s \right) \rightarrow 2 \ce{Hg} \left( l \right) + \ce{O_2} \left( g \right)\]

A reaction is also considered to be a decomposition reaction even when one or more of the products is still a compound. A metal carbonate decomposes into a metal oxide and carbon dioxide gas. For example, calcium carbonate decomposes into calcium oxide and carbon dioxide.

\[\ce{CaCO_3} \left( s \right) \rightarrow \ce{CaO} \left( s \right) + \ce{CO_2} \left( g \right)\]

Metal hydroxides decompose on heating to yield metal oxides and water. Sodium hydroxide decomposes to produce sodium oxide and water.

\[2 \ce{NaOH} \left( s \right) \rightarrow \ce{Na_2O} \left( s \right) + \ce{H_2O} \left( g \right)\]

A single-replacement reaction is a reaction in which one element replaces a similar element in a compound. The general form of a single-replacement (also called single-displacement) reaction is:

\[\ce{A} + \ce{BC} \rightarrow \ce{AC} + \ce{B}\]

In this general reaction, element $\ce{A}$ is a metal and replaces element $\ce{B}$, also a metal, in the compound. When the element that is doing the replacing is a nonmetal, it must replace another nonmetal in a compound, and the general equation becomes:

\[\ce{Y} + \ce{XZ} \rightarrow \ce{XY} + \ce{Z}\]

$\ce{Y}$ is a nonmetal and replaces the nonmetal $\ce{Z}$ in the compound with $\ce{X}$.

Magnesium is a more reactive metal than copper. When a strip of magnesium metal is placed in an aqueous solution of copper (II) nitrate, it replaces the copper. The products of the reaction are aqueous magnesium nitrate and solid copper metal.

\[\ce{Mg} \left( s \right) + \ce{Cu(NO_3)_2} \left( aq \right) \rightarrow \ce{Mg(NO_3)_2} \left( aq \right) + \ce{Cu} \left( s \right)\]

Many metals react easily with acids, and, when they do so, one of the products of the reaction is hydrogen gas. Zinc reacts with hydrochloric acid to produce aqueous zinc chloride and hydrogen (see figure below).

\[\ce{Zn} \left( s \right) + 2 \ce{HCl} \left( aq \right) \rightarrow \ce{ZnCl_2} \left( aq \right) + \ce{H_2} \left( g \right)\]

Figure 10.6.1: Zinc metal reacts with hydrochloric acid to give off hydrogen gas in a single-replacement reaction.

Figure 10.6.2: Pictured here is about 3 pounds of sodium metal reacting with water. Sodium metal reacts vigorously when dropped into a container of water, giving off hydrogen gas. A large piece of sodium will often generate so much heat that the hydrogen will ignite.

A double-replacement reaction is a reaction in which the positive and negative ions of two ionic compounds exchange places to form two new compounds. The general form of a double-replacement (also called double-displacement) reaction is:

\[\ce{AB} + \ce{CD} \rightarrow \ce{AD} + \ce{CB}\]

In this reaction, $\ce{A}$ and $\ce{C}$ are positively-charged cations, while $\ce{B}$ and $\ce{D}$ are negatively-charged anions. Double-replacement reactions generally occur between substances in aqueous solution. In order for a reaction to occur, one of the products is usually a solid precipitate, a gas, or a molecular compound such as water.

A precipitate forms in a double-replacement reaction when the cations from one of the reactants combine with the anions from the other reactant to form an insoluble ionic compound. When aqueous solutions of potassium iodide and lead (II) nitrate are mixed, the following reaction occurs.

\[2 \ce{KI} \left( aq \right) + \ce{Pb(NO_3)_2} \left( aq \right) \rightarrow 2 \ce{KNO_3} \left( aq \right) + \ce{PbI_2} \left( s \right)\]

Figure 10.6.3: When a few drops of lead (II) nitrate are added to a solution of potassium iodide, a yellow precipitate of lead (II) iodide immediately forms in a double-replacement reaction.

A combustion reaction is a reaction in which a substance reacts with oxygen gas, releasing energy in the form of light and heat. Combustion reactions must involve $\ce{O_2}$ as one reactant. The combustion of hydrogen gas produces water vapor (see figure below).

\[2 \ce{H_2} \left( g \right) + \ce{O_2} \left( g \right) + 2 \ce{H_2O} \left( g \right)\]

Notice that this reaction also qualifies as a combination reaction.

Figure 10.6.4: The Hindenburg was a hydrogen-filled airship that suffered an accident upon its attempted landing in New Jersey in 1937. The hydrogen immediately combusted in a huge fireball, destroying the airship and killing 36 people. The chemical reaction was a simple one: hydrogen combining with oxygen to produce water.

Many combustion reactions occur with a hydrocarbon, a compound made up solely of carbon and hydrogen. The products of the combustion of hydrocarbons are always carbon dioxide and water. Many hydrocarbons are used as fuel because their combustion releases very large amount of heat energy. Propane $\left( \ce{C_3H_8} \right)$ is a gaseous hydrocarbon that is commonly used as the fuel source in gas grills.

\[\ce{C_3H_8} \left( g \right) + 5 \ce{O_2} \left( g \right) \rightarrow 3 \ce{CO_2} \left( g \right) + 4 \ce{H_2O} \left( g \right)\]

Example 10.6.1

Ethanol can be used as a fuel source in an alcohol lamp. The formula for ethanol is $\ce{C_2H_5OH}$. Write the balanced equation for the combustion of ethanol.

Solution:

Step 1: Plan the problem.

Ethanol and oxygen are the reactants. As with a hydrocarbon, the products of the combustion of an alcohol are carbon dioxide and water.

Step 2: Solve.

Write the skeleton equations: $\ce{C_2H_5OH} \left( l \right) + \ce{O_2} \left( g \right) \rightarrow \ce{CO_2} \left( g \right) + \ce{H_2O} \left( g \right)$

Balance the equation.

\[\ce{C_2H_5OH} \left( l \right) + 3 \ce{O_2} \left( g \right) \rightarrow 2 \ce{CO_2} \left( g \right) + 3 \ce{H_2O} \left( g \right)\]

Step 3: Think about your result.

Combustion reactions must have oxygen as a reactant. Note that the water that is produced is in the gas state rather that the liquid state because of the high temperatures that accompany a combustion reaction.