South Pasadena • Chemistry
Name
Period
Date
5 · Chemical Reactions
STOICHIOMETRY
WORKSHEET
1. Nitrogen gas reacts with hydrogen gas, forming ammonia gas.
(a)
Write the balanced equation for the reaction.
N2 (g) + 3 H2 (g)  2 NH3 (g)
(b)
Find the molar masses of the substances in the reaction.
N2:
H2:
2(14.01) = 28.02 g/mol
2(1.008) = 2.016 g/mol
(c)
NH3:
1(14.01) + 3(1.008) = 17.03 g/mol
Find the moles of NH3 (g) formed when 5.00 moles of H2 (g) reacts.
GIVEN:
5.0 mol H2
DESIRED:
WORK:
ANSWER:
2 mol NH3
5.0 mol H2 
 3 mol H2  = 3.3 mol NH3
3.3 mol NH3
? mol NH3
(d)
Find the moles of H2 (g) required when 3.5 grams of N2 (g) reacts.
GIVEN:
WORK:
ANSWER:
3.5 g N2
1 mol N2  3 mol H2
3.5 g N2 
28.02 g N2 1 mol N2 = 0.37 mol H2
0.37 mol H2
DESIRED:
? mol H2
(e)
Find the grams of H2 (g) needed to form 21.1 grams of NH3 (g).
GIVEN:
WORK:
ANSWER:
21.1 g NH3
1 mol NH3   3 mol H2  2.016 g H2
21.1 g NH3 
17.03 g NH3 2 mol NH3  1 mol H2  = 3.75 g H2
3.75 g H2
DESIRED:
? g H2
(f)
Find the liters of NH3 (g) produced at STP when 9.62 grams of N2 (g) is used.
GIVEN:
WORK:
ANSWER:
9.62 g N2
1 mol N2  2 mol NH3 22.4 L NH3
9.62 g N2 
28.02 g N2  1 mol N2   1 mol NH3  = 15.4 L NH3
15.4 L NH3
DESIRED:
? L NH3
2. Solid potassium chlorate decomposes to form solid potassium chloride and oxygen gas.
(a)
Write the balanced equation for the reaction.
2 KClO3 (s)  2 KCl (s) + 3 O2 (g)
(b)
Find the molar masses of the substances in the reaction.
KClO3:
KCl:
O2:
1(39.10) + 1(35.45) + 3(16.00)
1(39.10) + 1(35.45 = 74.55 g/mol 2(16.00) = 32.00 g/mol
= 122.55 g/mol
Find the mass of KCl (s) produced when 42.0 grams of KClO3 (s) decomposes.
(c)
GIVEN:
WORK:
ANSWER:
42.0 g KClO3
1 mol KClO3   2 mol KCl  74.55 g KCl
42.0 g KClO3 
122.55 g KClO3 2 mol KClO3  1 mol KCl 
25.5 g KCl
DESIRED:
? g KCl
= 25.5 g KCl
(d)
Find the volume of O2 (g) produced at STP when 42.0 grams of KClO3 (s) decomposes.
GIVEN:
WORK:
ANSWER:
42.0 g KClO3
1 mol KClO3   3 mol O2  22.4 L O2
42.0 g KClO3 
122.55 g KClO3 2 mol KClO3  1 mol O2 
11.5 L O2
DESIRED:
? L O2
= 11.5 L O2
3. Zinc metal is placed in a solution of hydrochloric acid to form hydrogen gas and aqueous zinc chloride.
(a)
Write the balanced equation for the reaction.
Zn (s) + 2 HCl (aq)  H2 (g) + ZnCl2 (aq)
MM: 65.38
(b)
36.46
2.016
136.28
Find the mass of Zn (s) required to produce 12.6 L of H2 (g) at STP.
GIVEN:
WORK:
ANSWER:
12.6 L H2
1 mol H2  1 mol Zn 65.38 g Zn
12.6 L H2 
22.4 L H2  1 mol H2   1 mol Zn  = 36.8 g Zn
36.8 g Zn
DESIRED:
? g Zn
(c)
Calculate the moles of HCl (aq) required to produce 12.6 L of H2 (g) a STP.
GIVEN:
WORK:
ANSWER:
12.6 L H2
1 mol H2  2 mol HCl
12.6 L H2
22.4 L H2  1 mol H2  = 1.13 mol HCl
1.13 mol HCl
DESIRED:
? mol HCl
(d)
If the volume of HCl (aq) in part (c) is 1.20 L, calculate the concentration of the HCl solution.
VARIABLES:
WORK:
ANSWER:
n = 1.13 mol
V = 1.20 L
M=?
n 1.13 mol
M= =
= 0.938 M
V
1.20 L
0.938 M
4. A solution of lead acetate is combined with a solution of hydrochloric acid forming a lead chloride precipitate
and acetic acid.
(a) Write the balanced equation for the reaction.
Pb(C2H3O2)2 (aq) + 2 HCl (aq)  PbCl2 (s) + 2 HC2H3O2 (aq)
(b)
(c)
Find the molar masses of the substances in the reaction.
Pb(C2H3O2)2:
HCl:
PbCl2
1(207.2) + 4(12.01) + 6(1.008) + 1(1.008) + 1(35.45)
1(207.2) + 2(35.45)
4(16.00) = 325.29 g/mol
= 36.46 g/mol
= 278.10 g/mol
Find the mass of lead acetate required to react to form 94.5 g of lead chloride.
2(12.01) + 4(1.008) + 2(16.00)
= 60.05 g/mol
GIVEN:
WORK:
ANSWER:
94.5 g PbCl2
1 mol PbCl2 1 mol Pb(C2H3O2)2
94.5 g PbCl2
278.10 g PbCl2 1 mol PbCl2 
325.29 g Pb(C2H3O2)2= 111 g Pb(C2H3O2)2
 1 mol Pb(C2H3O2)2 
111 g
Pb(C2H3O2)2
DESIRED:
?g
Pb(C2H3O2)2
(d)
HC2H3O2:
Calculate the molecules of acetic acid produced when 94.5 g of lead chloride is formed.
GIVEN:
WORK:
94.5 g PbCl2
1 mol PbCl2 2 mol HC2H3O2
4.09 × 1023
94.5 g PbCl2
molecules
278.10 g PbCl2 1 mol PbCl2 
23
6.022 × 10 molecules HC2H3O2= 4.09 × 1023 molecules HC2H3O2 HC2H3O2
1 mol HC2H3O2


DESIRED:
? molecules
HC2H3O2
ANSWER: