How do you balance a single replacement reaction?

Question

Natalie Anton · Accepted Answer

The single replacement reaction equation is balanced in the same manner as any other equation by arranging the coefficients in front of the chemical formulas in such a way that the elemental numbers on both sides of the equation are equal.

First example.

#"Na"("s")# + #"ZnCl"_2("aq")"# #rarr"# #"NaCl"("aq")# + #"Zn"("s")#

First we notice that there are two Cl atoms on the left side of the equation and one on the right, so we add a coefficient of 2 in front of #"NaCl"#.

#"Na"("s")# + #"ZnCl"_2("aq")"# #rarr"# #"2NaCl"("aq")# + #"Zn"("s")#

We put a coefficient of two in front of the Na because there are now two Na atoms on the right side and only one on the left.

#"2Na"("s")# + #"ZnCl"_2("aq")"# #rarr"# #"2NaCl"("aq")# + #"Zn"("s")#

With equal quantities of each element on both sides of the equation, the equation is now balanced.

It is simpler to balance an equation that includes a polyatomic ion if you treat the polyatomic ion as a single unit.

#"Al"("s")# + #"CuSO"_4"("aq")# #rarr# #"Al"_2"(SO"_4)_3"("aq")# + #"Cu"("s")#

If you consider the polyatomic sulfate ion #"SO"_4^(2-)#. (Don't worry about the charge. The chemical formulas for the compounds containing the sulfate ion are correct.) If you look on the left side of the equation, there is one sulfate ion, and on the right side there are three sulfate ions. So place a coefficient of 3 in front of the #"CuSO"_4"("aq")#.

#"Al"("s")# + #"3CuSO"_4"("aq")# #rarr# #"Al"_2"(SO"_4)_3"(aq)# + #"Cu"("s")#

With two Al atoms on the right and one on the left, the Al must now be balanced. To do this, place a coefficient of two in front of the Al on the left.

#"2Al"("s")# + #"3CuSO"_4"("aq")# #rarr# #"Al"_2"(SO"_4)_3"(aq)# + #"Cu"("s")#

Since there are three Cu atoms on the left and one on the right, we must now balance the Cu by placing a coefficient of three in front of the Cu on the right.

#"2Al"("s")# + #"3CuSO"_4"("aq")# #rarr# #"Al"_2"(SO"_4)_3"(aq)# + #"3Cu"("s")#

At this point, the equation is balanced because there are the same number of polyatomic ions and atoms of each element on both sides.

Xavier Avery · Answer

undefined A single replacement reaction can be balanced by adjusting coefficients so that the number of atoms of each element on both sides of the chemical equation is the same.