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

Video ID: 1-32-1 © 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