4.1 Writing and Balancing Chemical Equations

What does it mean to say an equation is balanced? Why is it important for an equation to be balanced?

Balance the following equations:

(a) $\text{PCl}_{5} \left(s\right) + \text{H}_{2} \text{O} \left(l\right) \rightarrow \text{POCl}_{3} \left(l\right) + \text{HCl} \left(a q\right)$

(b) $\text{Cu} \left(s\right) + \text{HNO}_{3} \left(a q\right) \rightarrow \text{Cu} \left(\text{NO}_{3}\right)_{2} \left(a q\right) + \text{H}_{2} \text{O} \left(l\right) + \text{NO} \left(g\right)$

(c) $\text{H}_{2} \left(g\right) + \text{I}_{2} \left(s\right) \rightarrow \text{HI} \left(s\right)$

(d) $\text{Fe} \left(s\right) + \text{O}_{2} \left(g\right) \rightarrow \text{Fe}_{2} \text{O}_{3} \left(s\right)$

(e) $\text{Na} \left(s\right) + \text{H}_{2} \text{O} \left(l\right) \rightarrow \text{NaOH} \left(a q\right) + \text{H}_{2} \left(g\right)$

(f) $\left(\right. \text{NH}_{4} \left.\right)_{2} \text{Cr}_{2} \text{O}_{7} \left(s\right) \rightarrow \text{Cr}_{2} \text{O}_{3} \left(s\right) + \text{N}_{2} \left(g\right) + \text{H}_{2} \text{O} \left(g\right)$

(g) $\text{P}_{4} \left(s\right) + \text{Cl}_{2} \left(g\right) \rightarrow \text{PCl}_{3} \left(l\right)$

(h) $\text{PtCl}_{4} \left(s\right) \rightarrow \text{Pt} \left(s\right) + \text{Cl}_{2} \left(g\right)$

Write a balanced molecular equation describing each of the following chemical reactions.

(a) Solid calcium carbonate is heated and decomposes to solid calcium oxide and carbon dioxide gas.

(b) Gaseous butane, C₄H₁₀, reacts with diatomic oxygen gas to yield gaseous carbon dioxide and water vapor.

(c) Aqueous solutions of magnesium chloride and sodium hydroxide react to produce solid magnesium hydro…

Colorful fireworks often involve the decomposition of barium nitrate and potassium chlorate and the reaction of the metals magnesium, aluminum, and iron with oxygen.

(a) Write the formulas of barium nitrate and potassium chlorate.

(b) The decomposition of solid potassium chlorate leads to the formation of solid potassium chloride and diatomic oxygen gas. Write an equation for the reaction.

(c) The…

Aqueous hydrogen fluoride (hydrofluoric acid) is used to etch glass and to analyze minerals for their silicon content. Hydrogen fluoride will also react with sand (silicon dioxide).

(a) Write an equation for the reaction of solid silicon dioxide with hydrofluoric acid to yield gaseous silicon tetrafluoride and liquid water.

(b) The mineral fluorite (calcium fluoride) occurs extensively in Illinois…

From the balanced molecular equations, write the complete ionic and net ionic equations for the following:

(a) $\text{K}_{2} \text{C}_{2} \text{O}_{4} \left(a q\right) + \text{Ba} (\text{OH})_{2} \left(a q\right) \rightarrow 2 \text{KOH} \left(a q\right) + \text{BaC}_{2} \text{O}_{4} \left(s\right)$

(b) $\text{Pb} \left(\right. \left(\text{N} \text{O}_{3} \left.\right)\right)_{2} \left(a q\right) + \text{H}_{2} \text{SO}_{4} \left(a q\right) \rightarrow \text{PbSO}_{4} \left(s\right) + 2 \text{HNO}_{3} \left(a q\right)$

(c) $\text{CaCO}_{3} \left(s\right) + \text{H}_{2} \text{SO}_{4} \left(a q\right) \rightarrow \text{CaSO}_{4} \left(s\right) + \text{CO}_{2} \left(g\right) + \text{H}_{2} \text{O} \left(l\right)$