types of chemical reactions

single replacement reactions

A single replacement reaction occurs when one ion takes the place of another in a single compound. This type of reaction has the general equation: A + BC ! B + AC Do you see how A has replaced B in the compound? The compound BC has become the compound AC. An example of a single replacement reaction occurs when potassium (K) reacts with water (H2 O). A colorless solid called potassium hydroxide (KOH) forms, and hydrogen gas (H2 ) is released. The equation for the reaction is: 2K + 2H2 O ! 2KOH + H2 Potassium is a highly reactive group 1 alkali metal, so its reaction with water is explosive. You can actually watch this reaction occurring at: http://commons.wikimedia.org/wiki/File:Potassium_water_20.theora.ogv .

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combustion reactions

A combustion reaction occurs when a substance reacts quickly with oxygen (O2 ). You can see an example of a combustion reaction in Figure 8.10. Combustion is commonly called burning. The substance that burns is usually referred to as fuel. The products of a combustion reaction include carbon dioxide (CO2 ) and water (H2 O). The reaction typically gives off heat and light as well. The general equation for a combustion reaction can be represented by: Fuel + O2 ! CO2 + H2 O

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combustion example 1

The fuel that burns in a combustion reaction is often a substance called a hydrocarbon. A hydrocarbon is a compound that contains only carbon (C) and hydrogen (H). Fossil fuels, such as natural gas, consist of hydrocarbons. Natural gas is a fuel that is commonly used in home furnaces and gas stoves (see Figure 8.11). The main component of natural gas is the hydrocarbon called methane (CH4 ). The combustion of methane is represented by the equation: CH4 + 2O2 ! CO2 + 2H2 O

synthesis reactions

A synthesis reaction occurs when two or more reactants combine to form a single product. A synthesis reaction can be represented by the general equation: A+B !C In this general equation (and others like it in this lesson), the letters A, B,C, and so on represent atoms or ions of elements. The arrow shows the direction of the reaction. The letters on the left side of the arrow are the reactants that begin the chemical reaction. The letters on the right side of the arrow are the product of the reaction. Two examples of synthesis reactions are described below. You can see more examples at this URL:

double replacement reactions

A double replacement reaction occurs when two compounds exchange ions. This produces two new compounds. A double replacement reaction can be represented by the general equation: AB +CD ! AD +CB Do you see how B and D have changed places? Both reactant compounds have changed. An example of a double replacement reaction is sodium chloride (NaCl) reacting with silver fluoride (AgF). This reaction is represented by the equation: NaCl + AgF ! NaF + AgCl Cl and F have changed places. Can you name the products of this reaction?

decomposition example 2

Another example of a decomposition reaction is illustrated in Figure 8.9. Water (H2 O) decomposes to hydrogen (H2 ) and oxygen (O2 ) when an electric current passes through it. This reaction is represented by the equation: 2H2 O ! 2H2 + O2 What is the reverse of this decomposition reaction? (Hint: How is water synthesized? You can look at this chapters "Introduction to Chemical Reactions" lesson to find out.)

replacement reactions

Replacement reactions involve ions. They occur when ions switch places in compounds. There are two types of replacement reactions: single and double. Both types are described below.

decomposition reactions

A decomposition reaction is the reverse of a synthesis reaction. In a decomposition reaction, one reactant breaks down into two or more products. This can be represented by the general equation: AB ! A + B Two examples of decomposition reactions are described below. You can see other examples at this URL: http://w

decomposition example 1

An example of a decomposition reaction is the breakdown of carbonic acid (H2 CO3 ) to produce water (H2 O) and carbon dioxide (CO2 ). The equation for this reaction is: H2 CO3 ! H2 O + CO2 Carbonic acid is synthesized in the reverse reaction. It forms when carbon dioxide dissolves in water. For example, some of the carbon dioxide in the atmosphere dissolves in the ocean and forms carbonic acid. The amount of carbon dioxide in the atmosphere has increased over recent decades (see Figure 8.8). As a result, the acidity of ocean water is also increasing. How do you think this might affect ocean life?

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synthesis example 2

Another example of a synthesis reaction is illustrated in Figure 8.7. The brown haze in the air over the city of Los Angeles is smog. A major component of smog is nitrogen dioxide (NO2 ). It forms when nitric oxide (NO), from sources such as car exhaust, combines with oxygen (O2 ) in the air. The equation for this reaction is: 2NO + O2 ! 2NO2 Nitrogen dioxide is a toxic gas with a sharp odor. It can irritate the eyes and throat and trigger asthma attacks. It is a major air pollutant.

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synthesis example 1

An example of a synthesis reaction is the combination of sodium (Na) and chlorine (Cl) to produce sodium chloride (NaCl). This reaction is represented by the chemical equation: 2Na + Cl2 ! 2NaCl Sodium is a highly reactive metal, and chlorine is a poisonous gas (see Figure 8.6). The compound they synthesize has very different properties. It is table salt, which is neither reactive nor poisonous. In fact, salt is a necessary component of the human diet.

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combustion example 2

Your own body cells burn fuel in combustion reactions. The fuel is glucose (C6 H12 O6 ), a simple sugar. The process in which combustion of glucose occurs in body cells is called cellular respiration. This combustion reaction provides energy for life processes. Cellular respiration can be summed up by the equation: C6 H12 O6 + 6O2 ! 6CO2 + 6H2 O Where does glucose come from? It is produced by plants during photosynthesis. In this process, carbon dioxide and water combine to form glucose. Which type of chemical reaction is photosynthesis?

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instructional diagrams

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questions

one reactant breaking down into two or more products

a. synthesis reaction

b. combustion reaction

-->  c. decomposition reaction

d. single replacement reaction

e. double replacement reaction

f. burning

g. fuel

The general equation for a synthesis reaction is

a. AB  A + B

b. A + BC  B + AC

-->  c. A+BC

d. AB + C  A + BC

ions changing places in two compounds

a. synthesis reaction

b. combustion reaction

c. decomposition reaction

d. single replacement reaction

-->  e. double replacement reaction

f. burning

g. fuel

Which of the following is a decomposition reaction?

a. 2Na + Cl2  2NaCl

-->  b. 2H2 O  2H2 + O2

c. CH4 + O2  CO2 + H2 O

d. NaCl + AgF  NaF + AgCl

two reactants combining to form a single product

-->  a. synthesis reaction

b. combustion reaction

c. decomposition reaction

d. single replacement reaction

e. double replacement reaction

f. burning

g. fuel

Which type of reaction is represented by the following chemical equation? 2K + 2H2 O 2KOH + H2

a. double replacement

-->  b. single replacement

c. decomposition

d. synthesis

Which of the following is always a product of a combustion reaction?

-->  a. water

b. ashes

c. smoke

d. oxygen

substance reacting quickly with oxygen

a. synthesis reaction

-->  b. combustion reaction

c. decomposition reaction

d. single replacement reaction

e. double replacement reaction

f. burning

g. fuel

one of the reactants in a combustion reaction

a. synthesis reaction

b. combustion reaction

c. decomposition reaction

d. single replacement reaction

e. double replacement reaction

f. burning

-->  g. fuel

In living cells, energy is produced by the process called

a. photosynthesis.

b. sugar synthesis.

-->  c. cellular respiration.

d. glucose decomposition.

one ion taking the place of another in a compound

a. synthesis reaction

b. combustion reaction

c. decomposition reaction

-->  d. single replacement reaction

e. double replacement reaction

f. burning

g. fuel

another term for a combustion reaction

a. synthesis reaction

b. combustion reaction

c. decomposition reaction

d. single replacement reaction

e. double replacement reaction

-->  f. burning

g. fuel

Which of the following is an example of a synthesis reaction?

a. 2NO + O2  2NO2

b. 2Na + Cl2  2NaCl2

c. H2 O  H2 + O2

-->  d. two of the above

A decomposition reaction is represented by the general equation

a. A + B + C  AB + C.

b. A + BC  AB + C.

-->  c. AB  A + B

d. none of the above

Which type of reaction is represented by the following chemical equation? NaCl + AgF NaF + AgCl

a. synthesis

b. decomposition

c. single replacement

-->  d. double replacement

A synthesis reaction occurs when two or more reactants combine to form a single product.

-->  a. true

b. false

Which of the following is always a reactant in a combustion reaction?

a. water

-->  b. oxygen

c. carbon dioxide

d. two of the above

Another term for a combustion reaction is decomposition.

a. true

-->  b. false

Methane is a

a. hydrocarbon.

b. component of natural gas.

c. compound containing only carbon and hydrogen.

-->  d. all of the above

What do living cells use for fuel?

a. oxygen

b. water

-->  c. glucose

d. hydrocarbons

Fossil fuels such as oil and natural gas consist of hydrocarbons.

-->  a. true

b. false

The reaction in which carbon dioxide and water combine to form glucose

a. is a combustion reaction.

-->  b. is called photosynthesis.

c. takes place in all living cells.

d. all of the above

The fuel that cells use for energy is oxygen.

a. true

-->  b. false

Plants combine carbon dioxide and water to form glucose.

-->  a. true

b. false

Water decomposes when an electric current passes through it.

-->  a. true

b. false

A combustion reaction usually gives off heat and light.

-->  a. true

b. false

The burning of glucose in cells is called cellular combustion.

a. true

-->  b. false

Sodium chloride forms in a decomposition reaction.

a. true

-->  b. false

Methane and oxygen combine in a synthesis reaction.

a. true

-->  b. false

One product of the reaction in question 5 is carbon dioxide.

-->  a. true

b. false

There are two types of decomposition reactions.

a. true

-->  b. false

Carbon dioxide forms only in combustion reactions.

a. true

-->  b. false

The general equation AB + CD AD + CB represents a replacement reaction.

-->  a. true

b. false

The chemical reaction 2K + 2H2 O 2KOH + H2 is a replacement reaction.

-->  a. true

b. false

diagram questions

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