BCA table lecture

Stoichiometry 1
BCA Method
1.Lead will react with hydrochloric acid to
produce lead chloride and hydrogen gas.
How many moles of hydrochloric acid are
needed to completely react with 4.0 mole
of lead?
Equation:
Before:
Change:
After:
1. Lead will react with hydrochloric acid
to produce lead chloride and hydrogen
gas. How many moles of hydrochloric
acid are needed to completely react with
4.0 mole of lead?
1.Lead will react with hydrochloric acid to
produce lead chloride and hydrogen gas.
How many moles of hydrochloric acid are
needed to completely react with 4.0 mole
of lead?
Equation:
Pb +
2 HCl
→ PbCl 2
+ H 2
Equation:
Pb +
2 HCl
→ PbCl 2
+ H 2
Before:
Before:
4.0 mol
XS
0 mol
0 mol
Change:
Change:
After:
After:
1

What are the ratios?
Equation: Pb + 2 HCl → PbCl 2 + H 2
Pb : HCl is 1:2 ratio (you need twice (2/1) as much HCl)
Pb : PbCl 2 is 1:1 ratio
Pb : H 2 is 1:1 ratio
HCl : PbCl 2 is 2:1 ratio
HCl : H 2 is 2:1 ratio
PbCl 2 : H 2 is 1:1 ratio
1.Lead will react with hydrochloric acid to
produce lead chloride and hydrogen gas.
How many moles of hydrochloric acid are
needed to completely react with 4.0 mole
of lead?
Equation:
Before:
Change:
After:
Pb +
4.0 mol
-4.0 mol
2 HCl
XS
-8.0 mol
TWICE AS
MANY AS Pb
→ PbCl 2
0 mol
4.0 mol
+ H 2
0 mol
4.0 mol
Complete calculations on the side
1.Lead will react with hydrochloric acid to
produce lead chloride and hydrogen gas.
How many moles of hydrochloric acid are
needed to completely react with 4.0 mole
of lead?
In this case, desired answer is in
moles
If mass is required, convert moles
to grams in the usual way
Equation:
Before:
Change:
After:
Pb +
4.0 mol
-4.0 mol
0
2 HCl
XS
-8.0 mol
XS
→ PbCl 2
0 mol
4.0 mol
4.0 mol
+ H 2
0 mol
4.0 mol
4.0 mol
36.46g
8 .0moles HCl × = 291.68g
1mole
Sig Figs: 2.9 x 10 2 g
2

2. How many moles of hydrogen gas will be
produced if 2.5 moles of calcium hydride
react according to the following equation?
Equation:
Before:
Change:
After:
CaH 2 +
2 H 2 O →
Ca(OH) 2
+2 H 2
2. How many moles of hydrogen gas will be
produced if 2.5 moles of calcium hydride
react according to the following equation?
Equation:
Before:
Change:
After:
CaH 2 +
2.5 mol
2 H 2 O →
XS
Ca(OH) 2
0 mol
+2 H 2
0 mol
What are the ratios?
Equation: CaH 2 + 2 H 2 O → Ca(OH) 2 +2 H 2
CaH 2 : H 2 O is 1:2 ratio
CaH 2 : Ca(OH) 2 is 1:1 ratio
CaH 2 : H 2 is 1:2 ratio (you produce twice (2/1) as much H 2 )
H 2 O : Ca(OH) 2 is 2:1 ratio
H 2 O : H 2 is 2:2 ratio which reduces to 1:1
H 2 : Ca(OH) 2 is 2:1 ratio
2. How many moles of hydrogen gas will be
produced if 2.5 moles of calcium hydride
react according to the following equation?
Equation:
Before:
Change:
After:
CaH 2 +
2.5 mol
-2.5 mol
2 H 2 O →
XS
-5.0 mol
Ca(OH) 2
0 mol
2.5 mol
+2 H 2
0 mol
5.0 mol
TWICE AS
MUCH AS CaH 2
3

2. How many moles of hydrogen gas will be
produced if 2.5 moles of calcium hydride
react according to the following equation?
Equation:
Before:
Change:
After:
CaH 2 +
2.5 mol
-2.5 mol
0
2 H 2 O →
XS
-5.0 mol
XS
Ca(OH) 2
0 mol
2.5 mol
2.5 mol
+2 H 2
0 mol
5.0 mol
5.0 mol
Equation:
Before:
Change:
After:
3. How many moles of water will be
produced if 0.45 mol of oxygen reacts
according to the following equation?
2 C 6 H 6 +
15 O 2
→ 12 CO 2
+ 6 H 2 O
What are the ratios?
Equation:
Before:
Change:
After:
3. How many moles of water will be
produced if 0.45 mol of oxygen reacts
according to the following equation?
2 C 6 H 6 +
XS
15 O 2
0.45 mol
→ 12 CO 2
0 mol
+ 6 H 2 O
0 mol
Equation: 2 C 6 H 6 + 15 O 2 → 12 CO 2 + 6 H 2 O
C 6 H 6 : O 2 is 2:15 ratio
C 6 H 6 : CO 2 is 2:12 ratio = 1:6
C 6 H 6 : H 2 O is 2:6 ratio = 1:3
O 2 : CO 2 is 15:12 ratio
O 2 : H 2 O is 15:6 ratio = 5:2 (you produce 2/5 as much H 2 O)
CO 2 : H 2 O is 12:6 ratio = 2:1
4

Use Mole Ratios to Calculate
2 C 6 H 6 + 15 O 2 → 12 CO 2 + 6
H 2 O
15 mol O 2 will produce 6 mol H 2 O
6mol 2mol
H
O
0 .45mol
O
×
2
=
0.18mol
H
O
2
15mol
O
2
2
Equation:
Before:
Change:
After:
3. How many moles of water will be
produced if 0.45 mol of oxygen reacts
according to the following equation?
2 C 6 H 6 +
XS
-0.06 mol
15 O 2
0.45 mol
-0.45 mol
→ 12 CO 2
0 mol
0.36 mol
+ 6 H 2 O
0 mol
0.18 mol
2/5 AS MANY
AS O 2
Equation:
3. How many moles of water will be
produced if 0.45 mol of oxygen reacts
according to the following equation?
2 C 6 H 6 +
15 O 2
→ 12 CO 2
+ 6 H 2 O
Before:
XS
0.45 mol
0 mol
0 mol
Change:
-0.06 mol
-0.45 mol
0.36 mol
0.18 mol
After:
XS
0
0.36 mol
0.18 mol
5