A word about …. Single Replacement Reactions

Single Replacement Reactions A + BX  AX + B Element + Compound  New Element + New Compound A is replacing B in the compound – A is more active than B

Single Replacement Rxns 2 Li(s) + 2 H2O(l)  2 LiOH(aq) + H2(g) In this reaction, a metal replaces a hydrogen in a water molecule.

Single Replacement Rxns Another common type is when one metal replaces another metal in a compound. Cu(s) + 2 AgNO3(aq)  2 Ag(s) + Cu(NO3)2(aq) Copper replaced silver in the compound.

Single Replacement Rxns Finally, one nonmetal can replace another nonmetal in a compound. F2 + 2NaBr  2NaF + Br2 Fluorine replaced bromine in the compound.

Single Replacement Reactions Metals have different reactivities. You have to predict if a given metal and a given compound will react or not. You need an activity series, a list of elements organized by how easily they undergo certain chemical reactions.

Single Replacement Rxns Table J is an activity series. The more reactive a metal, the easier it loses its valence electrons. The most active metal is at the top. The least active metal is at the bottom. Use Table J to determine if a reaction will occur.

Single Replacement Rxns The rule is: A metal can replace any metal listed below it that is in a compound. It cannot replace any metal listed above it. The higher the metal, the more it wants to lose its electrons!

Ag(s) + Cu(NO3)2(aq)  ? What is the metal and the metal cation? Ag and Cu+2 Locate Ag and Cu in Table J. Ag is below Cu so this reaction will not go. Ag is less reactive than Cu.

Cu(s) + 2 AgNO3(aq)  ? What is the metal and the metal cation? Cu and Ag+1 Locate Cu and Ag in Table J. Cu is above Ag in Table J. Cu is more reactive than Ag. This reaction will go.  2 Ag(s) + 2 Cu(NO3)2(aq)

Single Replacement Reactions Table J can also be used to predict if A nonmetal replaces another nonmetal in a compound. Halogens are often the nonmetal. Nonmetals are WINNERS! So the nonmetals at the top of Table J want to gain electrons the most. Most active halogen = fluorine at top. Least active halogen = iodine at bottom.

Single Replacement Reactions The rule is: A more active halogen replaces a less active halogen that is part of a compound in aqueous solution. F2(g) + 2 NaBr(aq)  2 NaF(aq) + Br2(l) This reaction occurs because F2 is above Br2.

Single Replacement Reaction NR Br2(g) + 2 NaF(aq)  ? Br2 is below F2 in Table J. This reaction does not occur.

Summary If the “stand-alone” element is higher in Table J than the “like” element in the compound, the reaction will proceed.

Use Table J to predict if these reactions occur. K(s) + ZnCl2(aq)  Fe(s) + Na3PO4(aq)  Cu(s) + Mg(NO3)2(aq)  Al(s) + SnCl2(aq)  Ca(s) + KBr(aq)  Ti(s) + Pb(NO3)2(aq)  Cl2(g) + HF(aq)  F2(g) + CaI2(aq)  Yes No No Yes No Yes No Yes

Summary: Predicting Single Replacement Reactions Identify stand-alone element. Determine if stand-alone element is a metal or a nonmetal. (For the purposes of Table J, H2 is a metal.) Compare the stand-alone element to the corresponding element in the compound. If the stand-alone element is higher in Table J than the corresponding element in the compound, then the reaction occurs.

Next Step If the reaction proceeds, you have to figure out what the products are (say their names first, then write the formulas) and then balance the equation. If the reaction does not go, you just write NO REACTION.