College Chemistry : Identifying Reaction Types

Study concepts, example questions & explanations for College Chemistry

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Example Questions

Example Question #21 : Reactions

Which of the following is neither a product nor a reactant in a combustion reaction? 

Possible Answers:

All of these

Water

Oxygen

Hydrocarbons

Carbon Dioxide

Correct answer:

All of these

Explanation:

A combustion reaction involves the release of heat from the burning of a hydrocarbon in oxygen to form carbon dioxide and water. The amount of hydrogen, carbon, and oxygen are conserved. This reaction is exothermic because of the high energy released when organic hydrocarbons are burned. It can be easily observed in the burning of petroleum distillates such as gasoline. 

Example Question #22 : Reactions

Which type of reaction is shown?

Possible Answers:

Decomposition

Single displacement

Synthesis

Double displacement

Correct answer:

Double displacement

Explanation:

There are five main types of chemical reactions.

1) Synthesis reactions have the following format:

In these reactions, two substances combine to form one substance. This occurs when hydrogen and oxygen combine to form water: 

2) Decomposition reactions have the following format:

In these reactions, a compound breaks down to form smaller substances. This occurs when some acids decompose into an acidic oxide and water:

3) Single displacement reactions have the following format:

In these reactions, a single element replaces another element in a compound. This occurs in the reaction between zinc and hydrochloric acid:

4) Double displacement reactions have the following format:

In these reactions, an element from each of the two reactant compounds switches places. This occurs in the reaction between sulfuric acid and sodium hydroxide:

5) Combustion reactions have the following format:

In these reactions, a hydrocarbon and oxygen always react to form carbon dioxide and water. Here is an example:

Example Question #1 : Identifying Reaction Types

Identify the type of reaction that is given by the following equation:

Possible Answers:

Oxidation-reduction

Gas evolution

Precipitation

Acid-base

Correct answer:

Oxidation-reduction

Explanation:

Recall that combustion equations are examples of reduction-oxidation reactions.

This cannot be a precipitation reaction because there are no solids in the products.

This cannot be a gas-evolution reaction because the reactants are not in aqueous form.

This cannot be an acid-base reaction because there is no proton transfer.

Example Question #24 : Reactions

What type of reaction is shown?

Possible Answers:

Combustion

Double displacement/metathesis

Single displacement

Combination

Decomposition

Correct answer:

Combination

Explanation:

This is a basic identify the reaction type equation of the form:

Since both reactants are combined into one it is a combination reaction.

Now let's go over the wrong answers:

1) It isn't a single displacement because single displacement reactions are of the form:

2) It isn't a double displacement/metathesis reaction because double displacement reactions are of the form:

3) It isn't a decomposition reaction because decomposition reactions are the exact opposite of what occurs in the reaction in the problem. Meaning instead of two or more elements forming a compound, a compound breaks down into two or more elements.

4) It isn't a combustion reaction because a combustion reaction refers to the burning of a compound (usually a hydrocarbon) within which the other reactant is  and the products are some amount of . So the general form of a combustion equation look as follows:

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