1. Which of the following is a decomposition reaction?
QUESTION:
Which of the following is a decomposition reaction?
A. 2 CO(g) + O2(g)  2 CO2(g)
B. Mg(s) + 2 HCl(aq)  MgCl2(aq) + H2(g) C. Ba(OH)2(aq) + H2SO4(aq)  2 H2O(l) + BaSO4(s)
D. 2 H2O2(aq) 2 H2O(l) + O2(g)
Common types of Reactions
Decomposition: one reactant, two or more products
Combination or synthesis: one product, two or more reactants
Displacement or Single Replacement: element + compound  another element + compound
Metathesis: two compounds that produce ions aqueous solution “exchange partners” (also known as “double replacement” or “double decomposition”
Which of the following is a decomposition reaction?
A. 2 CO + O2  2 CO2
B. Mg + 2 HCl  MgCl2 + H2 C. BaCl2 + 2 AgNO3  Ba(NO3)2 + AgCl
D. 2 H2O2  2 H2O + O2
PAUSE
CLICK
Chemical reactions can be classified as ...
HIGHLIGHT types as they are mentioend
decomposition,...
combination or synthesis,...
displacement... or
metathesis
A decomposition reaction is one that involves the breakdown of one substance into two or more substances. It involves only one reactant and two or more products.
Therefore, the correct answer is D.
Of the choices given, choice D is the only one where this is the case.
In choice D, there is one reactant...hydrogen peroxide
HIGHLIGHT H2O2
and two products...water and oxygen
HIGHLIGHT H2O and O2
Let’s look at the other choices.
Choice A is an example of a combination or synthesis reaction. HIGHLIGHT Combination or synthesis.
In choice A, we have two reactants
HIGHLIGHT CO and O2
and one product
HIGHLIGHT CO2
Choice B is an example of a displacement or single replacement reaction.
HIGHLIGHT Displacement
In a displacement reaction, an element displaces another element from a compound.
So the reactants are an element,... such as magnesium in choice B HIGHLIGHT Mg sand a compound, such as hydrochloric acid in choice B.
HIGHLIGHT HCl
In choice B, the element magnesium displaces the element hydrogen from hydrochloric acid.
Magnesium ends up being part of a compound in the product...
HIGHLIGHT MgCl2
and hydrogen is liberated as a free element.
The reaction in choice C is an example of a metathesis reaction, which is also known as a double replacement or double decomposition reaction.
THis reaction typically involves two compounds in aqueous solution
HIGHLIGHT (aq) labels for Ba(OH)2 and H2SO4(aq)
Typically, an ion from one of the two compounds can combine with an ion from the other compound to form a molecular compound such as water
or an ionic compound that is insoluble in water.
In the example given here, barium ions from barium hydroxide
HIGHLIGHT Ba in Ba(OH)2
combine with sulfate ions from sulfuric acid
HIGHLIGHT SO4 in H2SO4
to form barium sulfate
HIGHLIGHT BaSO4
which is insoluble in water. The fact that barium sulfate is insoluble is indicated here by the solid label.
HIGHLIGHT (s) in BaSO4(s)
Here, barium sulfate is called a precipitate.
CALLOUT “Precipitate” pointing to BaSO4(s)
The reaction in choice C is also called an acid-base neutralization reaction. Barium hydroxide is base
CALLOUT “base” pointing to Ba(OH)2
and H2SO4 is an acid.... sulfuric acid.
CALLOUT “acid” pointing to H2SO4
Anytime you mix an acid and a base, you get water
CALLOUT “water” pointing to H2O
and a salt. The salt in this case is barium sulfate
CALLOUT “salt” pointing to barium sulfate
Water molecules are formed when hydroxide ions
HIGHLIGHT OH in Ba(OH)2
combine with hydrogen ions
HIGHLIGHT H in H2SO4
CLICK PAUSE END RECORDING

2. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08