What type of reaction occurs when two or more simple substances combine to form a more complex one?

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.

There are many chemical reactions, however, they can be classify into four general types: synthesis, decomposition, single replacement and double replacement reactions.

Synthesis or Combination Reaction

In a synthesis reaction two or more simple substances combine to form a more complex substance: Two or more reactants and only one product.Ex: 2 H2 + O2 -----> 2 H2O 2 Reactants -----> 1 product

Decomposition Reaction

In a decomposition reaction one complex substance breaks down into its more simple parts. This is the opposite of a synthesis reaction. One reactant yields two or more products.Ex: 2 H2O -----> 2 H2 + O2 1 reactant -----> 2 products

Single displacement reaction

In a single replacement reaction an uncombined element replaces another in a compound. Two reactants yield two products.Ex: 2 HCl + Zn -----> ZnCl2 + H2

2 reactants ----->2 products

Double displacement reaction

In a double replacement reaction two elements forming part of two different compounds switch places to form a new compound. Two reactants yield two products.Ex: HCl + NaOH ----->NaCl + H2O

2 reactants-----> 2 products

A wheel rim is not very useful by itself. Driving on the rim can damage it and make for a very rough ride. When the rim is combined with a tire, the product can be put on a car and used for a safe and comfortable ride. The two separate items combine to make something that improves the car ride.

A combination 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:

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

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

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

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.

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

Sulfur reacts with oxygen to form sulfur dioxide.

\[\ce{S} \left( s \right) + \ce{O_2} \left( g \right) \rightarrow \ce{SO_2} \left( g \right)\nonumber \]

When nonmetals react with one another, the product is a molecular compound. Often, the nonmetal reactants can combine in different ratios and produce different products. Sulfur can also combine with oxygen to form sulfur trioxide.

\[2 \ce{S} \left( s \right) + 3 \ce{O_2} \left( g \right) \rightarrow 2 \ce{SO_3} \left( g \right)\nonumber \]

Transition metals are capable of adopting multiple positive charges within their ionic compounds. Therefore, most transition metals are capable of forming different products in a combination reaction. Iron reacts with oxygen to form both iron (II) oxide and iron (III) oxide:

\[2 \ce{Fe} \left( s \right) + \ce{O_2} \left( g \right) \rightarrow 2 \ce{FeO} \left( s \right)\nonumber \]

\[4 \ce{Fe} \left( s \right) + 3 \ce{O_2} \left( g \right) \rightarrow 2 \ce{Fe_2O_3} \left( s \right)\nonumber \]

Potassium is a very reactive alkali metal that must be stored under oil in order to prevent it from reacting with air. Write the balanced chemical equation for the combination reaction of potassium with oxygen.

Solution

Make sure formulas of all reactants and products are correct before balancing the equation. Oxygen gas is a diatomic molecule. Potassium oxide is an ionic compound and so its formula is constructed by the crisscross method. Potassium as an ion becomes $\ce{K^+}$, while the oxide ion is $\ce{O^{2-}}$.

The skeleton (unbalanced) equation:

\[\ce{K} \left( s \right) + \ce{O_2} \left( g \right) \rightarrow \ce{K_2O} \left( s \right) \nonumber\nonumber \]

The equation is then easily balanced with coefficients.

\[4 \ce{K} \left( s \right) + \ce{O_2} \left( g \right) \rightarrow 2 \ce{K_2O} \left( s \right) \nonumber\nonumber \]

Formulas are correct and the resulting combination reaction is balanced.

Can you build a balanced, combination reaction for the formation of aluminum oxide (Al2O3)?

Answer

4Al + 3O2 → 2Al2O3

Combination reactions can also take place when an element reacts with a compound to form a new compound composed of a larger number of atoms. Carbon monoxide reacts with oxygen to form carbon dioxide, according to the equation:

\[2 \ce{CO} \left( g \right) + \ce{O_2} \left( g \right) \rightarrow 2 \ce{CO_2} \left( g \right)\nonumber \]

Two compounds may also react to form a more complex compound. A very common example is the reaction of an oxide with water. Calcium oxide reacts readily with water to produce an aqueous solution of calcium hydroxide.

\[\ce{CaO} \left( s \right) + \ce{H_2O} \left( l \right) \rightarrow \ce{Ca(OH)_2} \left( aq \right)\nonumber \]

Sulfur trioxide gas reacts with water to form sulfuric acid. This is an unfortunately common reaction that occurs in the atmosphere in some places where oxides of sulfur are present as pollutants. The acid formed in the reaction falls to the ground as acid rain.

\[\ce{SO_3} \left( g \right) + \ce{H_2O} \left( l \right) \rightarrow \ce{H_2SO_4} \left( aq \right)\nonumber \]

Figure $\PageIndex{2}$: Acid rain has severe consequences on both natural and manmade objects. Acid rain degrades marble statues like the one on the left (A). The trees in the forest on the right (B) have been killed by acid rain. (Credit: (A) Nipik; (B) Nino Barbieri; Source: (A) http://commons.wikimedia.org/wiki/File:Acid_rain_woods1.JPG(opens in new window); (B) http://commons.wikimedia.org/wiki/File:Pollution_-_Damaged_by_acid_rain.jpg(opens in new window); License: (A) Public Domain; (B) CC by 2.5(opens in new window))