In terms of chemistry, what do a burning candle, a speeding car, and a sleeping kitten have in common?
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Figure 27 A burning candle, a speeding car, and a sleeping kitten all carry out the same type of chemical reaction.
In answering this question, consider the following: All are made of matter, all consist of atoms, and all are associated with at least one chemical reaction. Actually, the last property mentioned is one with an important overlap—all three things carry out the same type of chemical reaction. In this section, you will learn about different types of chemical reactions and how you can recognize them.
Patterns in Chemical Reactions
Chemists group similar reactions together according to specific patterns. This helps them classify the huge number of chemical reactions they deal with and consequently facilitate their work. Two reactions are similar if they share a pattern. Some patterns have to do with the number of reactants or the number of products in a reaction. For example, the following two reactions are similar in having only one reactant:
Other patterns are based on an exchange of atoms between reactants that follow a similar rearrangement. Still other patterns repeat the same reactant in every reaction. The two reactions shown below share a common reactant, O2.
Chemists identify patterns by comparing the balanced chemical equations for many reactions and noting similarities. They also think about what is accomplished by each reaction and how that compares to what is accomplished by other reactions that have similar patterns in their chemical equations.
Synthesis Reactions
One type of reaction is a synthesis reaction. The word synthesis means to combine or build. A synthesis reaction is one in which two or more reactants combine to form one compound as a product. The diagram below gives a symbolic representation of this pattern.
Synthesis reactions may use elements or compounds as reactants, but the product is always a compound. A compound can be formed as the result of combining two or more elements or compounds. Some examples of synthesis reactions are listed in the table below.
  Decomposition Reactions
Another type of reaction is a decomposition reaction. The word decomposition means to break down or divide. A decomposition reaction involves one compound breaking into two or more smaller compounds or elements. The diagram below gives a symbolic representation of this pattern.
Note that decomposition reactions have the opposite pattern from that found in synthesis reactions. Some examples are listed below. If you compare these reactions, you will see that all reactions involve the same pattern of one compound breaking down to form two or more products. The reactant is always a compound, and the products are either elements, compounds, or a combination of both.
  Combustion Reactions
A third reaction type is the combustion reaction. The word combustion means the process of burning. A combustion reaction involves the burning of elements or compounds in the presence of oxygen with the release of energy. The basic pattern of a combustion reaction is shown below.
In a combustion reaction, one reactant is always oxygen and the reaction is always exothermic.
In this case, we have a pattern in which one of the reactants is always the same. In addition, the products are always compounds. The table below lists some examples of combustion reactions.
The three images presented at the beginning of this section are all examples of combustion reactions. Let’s review them:
In the case of the candle, wax reacts with oxygen to produce carbon dioxide and water vapor. You can understand why a candle seems to disappear as it burns when you consider that the two products of this combustion reaction are gases.
A car uses gasoline as a fuel. Inside the car’s engine, the gasoline combines with oxygen in a combustion reaction to produce carbon dioxide and water vapor. The energy released by this reaction is what powers the car.
A sleeping kitten does not look as though it is burning anything, yet its cells are busy burning glucose in the combustion process called cellular respiration. The kitten breathes in oxygen, which is delivered to cells by the blood. Inside the cells, oxygen reacts with glucose during cellular respiration. The products of this process are carbon dioxide, which is eliminated through the lungs, and water, which is eliminated in urine and perspiration.
Replacement Reactions |
A fourth group of reactions includes the replacement reactions. In a replacement reaction, one or two elements replace other elements in compounds. If one element replaces another in a compound, the reaction is a single-replacement reaction. If two elements in two compounds change places to replace each other, the reaction is a double-replacement reaction. Note that, in addition to elements, polyatomic ions composed of groups of atoms may also be exchanged. Common examples are nitrate ion, NO3–, and ammonium ion, NH4+.
We will look more closely at single-replacement reactions first and double-replacement reactions a bit later. The basic pattern of a single replacement reaction is shown below.
An example of a single-replacement reaction is the reaction between iron and lead nitrate:
Note that iron (Fe) replaces lead (Pb) in the reaction.
In a single-replacement reaction, one element replaces another element to form a new compound. In a double-replacement reaction, two elements in two compounds replace each other to form two new compounds. The basic pattern of a double-replacement reaction is shown below.
An example of a double-replacement reaction is the reaction between silver nitrate and sodium chloride:
In this reaction, silver ion (Ag+) and sodium ion (Na+) replace each other by trading places. It could also be said that NO3– and Cl– replace each other.
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| Figure 35 The formations hanging inside a cave result from a double-replacement reaction taking place in ground water. Calcium and sodium replace each other in a reaction that forms calcium carbonate, which precipitates as water drips into the cave. |
Al2(CO3)3 → Al2O3 + 3CO2
a combustion reaction
a decomposition reaction
a synthesis reaction
a single-replacement reaction
a double-replacement reaction
answer :
a decomposition reaction
Response:
That's the correct answer
What is the type of the reaction below?
Mg + 2AgNO3 → 2Ag + Mg(NO3)2
a single-replacement reaction
a double-replacement reaction
a synthesis reaction
a decomposition reaction
a combustion reaction
Mg + 2AgNO3 → 2Ag + Mg(NO3)2
a single-replacement reaction
a double-replacement reaction
a synthesis reaction
a decomposition reaction
a combustion reaction
End of Chapter 3
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