3.51P - Chemistry: Molecular Nature Of Matter And Change

Question

Write balanced equations for each of the following by inserting the correct coefficients in the blanks:  

1. $\mathbf{\_Cu}\left(s\right)\mathbf{+}{\mathbf{\_S}}_{\mathbf{8}}\left(s\right)\mathbf{\to }{\mathbf{\_Cu}}_{\mathbf{2}}\mathbf{S}\left(s\right)$
2. ${\mathbf{\_P}}_{\mathbf{4}}{\mathbf{O}}_{\mathbf{10}}\left(s\right)\mathbf{+}{\mathbf{\_H}}_{\mathbf{2}}\mathbf{O}\left(l\right)\mathbf{\to }{\mathbf{\_H}}_{\mathbf{3}}{\mathbf{PO}}_{\mathbf{4}}\left(l\right)$
3. ${\mathbf{\_B}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{3}}\left(s\right)\mathbf{+}\mathbf{\_NaOH}\left(\mathrm{aq}\right)\mathbf{\to }{\mathbf{\_Na}}_{\mathbf{3}}{\mathbf{BO}}_{\mathbf{3}}\left(\mathrm{aq}\right)\mathbf{+}{\mathbf{\_H}}_{\mathbf{2}}\mathbf{O}\left(l\right)$
4. ${\mathbf{\_CH}}_{\mathbf{3}}{\mathbf{NH}}_{\mathbf{2}}\left(g\right)\mathbf{+}{\mathbf{\_O}}_{\mathbf{2}}\left(g\right)\mathbf{\to }{\mathbf{\_CO}}_{\mathbf{2}}\left(g\right)\mathbf{+}{\mathbf{\_H}}_{\mathbf{2}}\mathbf{O}\left(g\right)\mathbf{+}{\mathbf{\_N}}_{\mathbf{2}}\left(g\right)$
   

Step-by-Step Solution

Answer

1. $16\mathrm{Cu}\left(\mathrm{s}\right)+{\mathrm{S}}_8\left(\mathrm{g}\right)\to 8{\mathrm{Cu}}_2\mathrm{S}\left(\mathrm{s}\right)$
2. ${\mathrm{P}}_4{\mathrm{O}}_{10}\left(\mathrm{s}\right)+6{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to 4{\mathrm{H}}_3{\mathrm{PO}}_4\left(\mathrm{l}\right)$
3. ${\mathrm{B}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+6\mathrm{NaOH}\left(\mathrm{aq}\right)\to 2{\mathrm{Na}}_3{\mathrm{BO}}_3\left(\mathrm{aq}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$
   
4. $2{\mathrm{CH}}_3{\mathrm{NH}}_2\left(\mathrm{g}\right)+4{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{CO}}_2\left(\mathrm{g}\right)+4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)+{\mathrm{N}}_2\left(\mathrm{g}\right)$

Step1. Considering the following chemical equations:

1. $16\mathrm{Cu}\left(\mathrm{s}\right)+{\mathrm{S}}_8\left(\mathrm{s}\right)\to 8{\mathrm{Cu}}_2\mathrm{S}\left(\mathrm{s}\right)$
2. ${\mathrm{P}}_4{\mathrm{O}}_{10}\left(\mathrm{s}\right)+6{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to 4{\mathrm{H}}_3{\mathrm{PO}}_4\left(\mathrm{l}\right)$
   
3. ${\mathrm{B}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+6\mathrm{NaOH}\left(\mathrm{aq}\right)\to 2{\mathrm{Na}}_3{\mathrm{BO}}_3\left(\mathrm{aq}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$
   
4. $2{\mathrm{CH}}_3{\mathrm{NH}}_2\left(\mathrm{g}\right)+4{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{CO}}_2\left(\mathrm{g}\right)+4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)+{\mathrm{N}}_2\left(\mathrm{g}\right)$
   

Above is the final balanced equations.

Step2. The following points define which types of information does a balanced chemical equation provides:

1). Identification of reactants and products

Example. In the above reactions, $\mathrm{Cu}$,${\mathrm{S}}_8,{\mathrm{P}}_4{\mathrm{O}}_{10},{\mathrm{H}}_2\mathrm{O},{\mathrm{B}}_2{\mathrm{O}}_3,\mathrm{NaOH},{\mathrm{CH}}_3{\mathrm{NH}}_2, {\mathrm{andO}}_2$are reactants, and ${\mathrm{Cu}}_2\mathrm{S}, {\mathrm{H}}_3{\mathrm{PO}}_4, {\mathrm{Na}}_3{\mathrm{BO}}_3, {\mathrm{H}}_2\mathrm{O}, {\mathrm{CO}}_2, {\mathrm{N}}_2$  are products.

2). Physical states of reactants and products.

Example. (s) solid, (g) gas, (l) liquid, and (aq) solution.