Page 142 - Theory and Problems of BEGINNING CHEMISTRY

CHAP. 8] CHEMICAL EQUATIONS 131

8.15. Balance the following chemical equations:

(a)Pb(NO 3 ) 2 + KI −→ PbI 2 + KNO 3 (d)NH 3 + CuCl 2 −→ Cu(NH 3 ) 4 Cl
(b)H 2 S + CuCl 2 −→ HCl + CuS (e)As 2 S 3 + Na 2 S −→ NaAsS 2
(c)Hg Cl 2 + NH 3 −→ HgNH Cl + Hg + NH 4 Cl
2
2
Ans. (a)Pb(NO 3 ) 2 + 2KI −→ PbI 2 + 2 KNO 3 (d)4 NH 3 + CuCl 2 −→ Cu(NH 3 ) 4 Cl
(b)H 2 S + CuCl 2 −→ 2 HCl + CuS (e) As 2 S 3 + Na 2 S −→ 2 NaAsS 2
(c) Hg Cl 2 +2NH 3 −→ HgNH Cl+Hg+NH 4 Cl
2
2
8.16. Why is the catalyst not merely placed on both sides of the arrow, since it comes out of the reaction with
the same composition as it started with?
Ans. That would imply a certain mole ratio to the other reactants and products, which is not correct.

PREDICTING THE PRODUCTS OF A REACTION
8.17. In the list of reactivities of metals, Table 8-1, are all alkali metals more reactive than all alkaline earth
metals, or are all elements of both groups of metals more active than any other metals?
Ans. Both groups of metals are more active than any other metals. Actually, some alkaline earth metals are more
active than some alkali metals, and vice versa.

8.18. (a) What type of reaction requires knowledge of reactivities of elements? (b) What type requires knowl-
edge of solubility properties of compounds?
Ans. (a) Substitution reaction (b) Double-substitution reaction

8.19. Complete and balance the following equations:

(a)CH 4 + O 2 (limited amount) −→ (b)CH 4 + O 2 (excess amount) −→

Ans. (a) 2CH 4 + 3O 2 (limited amount) −→ 2CO + 4H 2 O
If suffient O 2 is available, CO 2 is the product.
(b) CH 4 + 2O 2 (excess amount) −→ CO 2 + 2H 2 O

8.20. What type of chemical reaction is represented by each of the following? Complete and balance the
equation for each.
(a)Cl 2 + AlBr 3 −→ (d) FeCl 2 + AgC H 3 O 2 −→
2
(b)Cl 2 + K −→ (e)C 3 H 8 + O 2 (limited) −→
(c)Na + AlCl 3 −→
Ans. (a) Substitution 3 Cl 2 + 2 AlBr 3 −→ 2 AlCl 3 + 3Br 2
(b) Combination Cl 2 + 2K −→ 2 KCl
(c) Substitution 3 Na + AlCl 3 −→ Al + 3 NaCl
(d) Double substitution FeCl 2 + 2 AgC H 3 O 2 −→ Fe(C 2 H 3 O 2 ) 2 + 2 AgCl
2
(e) Combustion 2 C 3 H 8 + 7O 2 −→ 6CO + 8H 2 O
8.21. What type of chemical reaction is represented by each of the following? Complete and balance the
equation for each.

(a)Cl 2 + CrCl 2 −→ (d) AlCl 3 + Cl 2 −→
(b)CO + O 2 −→ (e)C 5 H 12 + O 2 (limited quantity) −→
heat
(c) MgCO −→
3