AVOGADRO’S LAW / IDEAL GAS / STOICHIOMETRY PROBLEMS
1) If 0.950 mol of O2 has a volume of 20.0 L at some temperature and pressure, what would be the volume of 1.350
mol of O2?
n1 = 0.950 mol
V1 = 20.0 L
V2 = ?
n2 = 1.350 mol
V1 V2
=
n1 n2
V2 =
V1 n2
(20.0 L)(1.350 mol)
=
n1
0.950 mol
V2 = 28.4 L
2) If 0.500 mol N2(g) has a volume of 11.0 L at some temperature and pressure, what volume would 0.750 mol
CO2(g) have at the same temperature and pressure?
n1 = 0.500 mol N2
V1 = 11.0 L N2
V2 = ?
n2 = 0.750 mol CO2
V1 V2
=
n1 n2
V2 =
V1 n2
(11.0L N2 )(0.750 mol CO2 )
=
n1
0.500 mol N2
V2 = 16.5 L CO2
3) What is the volume of a 1 mol of a gas at STP?
V=?
n = 1 mol
T = 273.15 K
P = 1 atm
PV = nRT
V=
L·atm
)(273.15 K)
nRT (1 mol)(0.08206 mol·K
=
P
1 atm
V = 22.41 L
4) Determine the volume of 3.30 mol of a gas at 25°C and 0.995 atm.
V=?
n = 3.30 mol
T = 25°C = 298 K
P = 0.995 atm
PV = nRT
V=
L·atm
)(298 K)
nRT (3.30 mol)(0.08206 mol·K
=
P
0.995 atm
V = 81.1 L
5) Determine the temperature, in °C, if 10.0 g CO2 fills a 2.35 L container at 745 torr.
T=?
g = 10.0 g CO2
V = 2.35 L
1 atm
P = 745 torr (
) = 0.980 atm
PV =
gRT
MM
PV(MM) = gRT
760 torr
T=
g
)
PV(MM) (0.980 atm)(2.35 L)(44.01 mol
=
L·atm
gR
(10.0 g)(0.08206 mol·K)
T = 124 K = -149°C
6) Determine the molar mass of a gas if 0.500 g of it fills a 1500. mL container at 1.02 atm and 30.5°C.
MM = ?
g = 0.500 g
V = 1500. mL = 1.500 L
P = 1.02 atm
T = 30.5°C = 303.6 K
PV =
gRT
MM
PV(MM) = gRT
MM =
L·atm
)(303.6 K)
gRT (0.500 g)(0.08206 mol·K
=
PV
(1.02 atm)(1.500 L)
MM = 8.14
g
mol
7) For the reaction N2(g) + 3H2(g) → 2NH3(g), if 2.25 L H2 reacts, what volume of NH3 forms if both are at the same
temperature and pressure?
2 mol NH3
2.25 L H2 (
) = 1.50 L NH3
3 mol H2
8) For the reaction: Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g), if 10.0 g Zn reacts at STP, what volume of H2 forms?
1 mol Zn
1 mol H2 22.4 L H2
10.0 g Zn (
)(
)(
) = 3.43 L H2
65.38 g Zn 1 mol Zn 1 mol H2
9) For the reaction: CH4(g) + 2O2(g) → CO2(g) + 2H2O(g), if 15.00 L of CH4 is burned with excess O2 at 23°C and
1.05 atm, what mass of H2O is produced?
Find molar V at this T and P:
PV = nRT
V=
15.00 L CH4 (
L·atm
)(296 K)
nRT (1 mol)(0.08206 mol·K
=
= 23.1 L
P
1.05 atm
1 mol CH4
2 mol H2 O 18.02 g H2 O
)(
)(
) = 23.4 g H2 O
23.1 L CH4 1 mol CH4
1 mol H2 O
There are basically 3 types of stoichiometry situations involving gases.
Situation
What you need to do.
1)
same T and P
Multiply the given volume by the mole ratio between the two gases.
2)
at STP
Use 22.4 L as the molar V of the gas when volume is used in the calculation.
3)
not at STP
Find the molar volume for the given T and P using PV = nRT and then use that as the
molar volume in the stoichiometry calculation.