CHEM 103 EXAM 2 QUESTIONS AND
ANSWERS||A+ SOLUTION GUIDE
COMPLETE 100% CORRECT RATED A+
Concept: Density of Gases A: ✔️✔️ For a gas, density is directly proportional to
its mass and the surrounding pressure, but it shares an inverse relationship with
the temperature.
When measured under the same set of
conditions, which gas is expected to have the
highest density?
A. O2
B. Xe
C. He
D. They would all be the same -ANSWER ✔️✔️B. Higher mass=higher density
What mass of sodium azide, NaN3, (molar mass =
65.01 g/mol) is required to inflate a 45.5 L airbag to a
pressure of 828 mmHg at 20.0
oC?
A. 201 g
B. 2.06 g
C. 0.0317 g
D. 132 g
E. 89.3 g -ANSWER ✔️✔️E. 89.3 g
44.0 grams of gas at STP occupies 22.4 L.
The gas could be
A. O2
,B. N2
C. CO2
D.Ar -ANSWER ✔️✔️CO2: molar mass is 44 g and because of STP
PV=nRT
(1)(22.4)=(.08206)(273.15)n
n=1 mole
What happens to the density of a gas in a
sealed glass flask if the temperature is raised?
A. Density will increase.
B. Density will decrease.
C. Density will remain the same -ANSWER ✔️✔️C. Pressure and temperature
increase by the same ratio
d=pm/RT
A 1.00 L flask contains a mixture of Ar, N2 and
O2. If PTotal = 4.5 atm, and PAr = PO2 = 1.0 atm, what is PN2?
A. 1.0 atm
B. 1.5 atm
C. 2.5 atm
D. Cannot be determined unless
temperature is given -ANSWER ✔️✔️C. Ptotal = PAr + PO2 + PN2
4.5 = 1 + 1 + PN2
PN2 = 2.5
A 1.00 L flask contains a mixture of Ar, N2, and O2.
If PTotal = 4.5 atm, and PAr = PO2 = 1.0 atm, what is the volume occupied by
the oxygen?
,A. 0.22 L
B. 0.56 L
C. 1.00 L
D. Cannot be determined unless
temperature is given -ANSWER ✔️✔️C. Occupies entire flask even when part of
a mixture
Gas Mixtures: Key Concepts -ANSWER ✔️✔️Ptotal = PAr + PO2 + PN2
Pgas = (ngas/ntotal) * Ptotal
ngas/ntotal = Xgas, mole fraction
*a gas that makes up 21% or .21 of a mixture will contribute 21% of the total
pressure*
A 1.00 L flask contains a mixture of Ar, N
2, and O2.
If PTotal = 4.5 atm, and PAr = PO2 = 1.0 atm, what is the mole fraction of Ar?
A. 0.22
B. 0.56
C. 1.00
D. Cannot be determined unless
temperature is given -ANSWER ✔️✔️A. PV = nRT
PAr/Ptotal
1.0/4.5
If more N2 is introduced into the same flask so
that its partial pressure increases to 4.0 atm,
what happens to PO2?
, A. It increases
B. It decreases
C. It stays the same -ANSWER ✔️✔️C. It stays the same
CH4 and O2 are mixed in a stoichiometric
ratio in a glass flask, the total pressure in the
flask is 600 mmHg. What is the partial pressure
of each gas prior to combustion?
To determine the "stoichiometric ratio",
we need a balanced chemical equation.
What is it? -ANSWER ✔️✔️CH4 + 2O2 = CO2 + H2O
CH4 and O2 are mixed in a stoichiometric ratio in a
glass flask, the total pressure in the flask is 600
mmHg. What is the partial pressure of each gas prior
to combustion?
balanced chemical equation is: CH4 + 2O2 = CO2 + H2O
A. PO2 = 600 mmHg PCH4 = 600 mmHg
B. PO2 = 300 mmHg PCH4 = 300 mmHg
C. PO2 = 400 mmHg PCH4 = 200 mmHg
D. PO2 = 450 mmHg PCH4 = 150 mmHg -ANSWER ✔️✔️C. 2:1 mole ratio
between O2 and CH4 = 600
PO2 = 400
PCH4 = 200
The pressure of O2 in a 2.50 L flask is 3.0 atm. When
the stopcock connecting the flask to an empty 1.5 L
ANSWERS||A+ SOLUTION GUIDE
COMPLETE 100% CORRECT RATED A+
Concept: Density of Gases A: ✔️✔️ For a gas, density is directly proportional to
its mass and the surrounding pressure, but it shares an inverse relationship with
the temperature.
When measured under the same set of
conditions, which gas is expected to have the
highest density?
A. O2
B. Xe
C. He
D. They would all be the same -ANSWER ✔️✔️B. Higher mass=higher density
What mass of sodium azide, NaN3, (molar mass =
65.01 g/mol) is required to inflate a 45.5 L airbag to a
pressure of 828 mmHg at 20.0
oC?
A. 201 g
B. 2.06 g
C. 0.0317 g
D. 132 g
E. 89.3 g -ANSWER ✔️✔️E. 89.3 g
44.0 grams of gas at STP occupies 22.4 L.
The gas could be
A. O2
,B. N2
C. CO2
D.Ar -ANSWER ✔️✔️CO2: molar mass is 44 g and because of STP
PV=nRT
(1)(22.4)=(.08206)(273.15)n
n=1 mole
What happens to the density of a gas in a
sealed glass flask if the temperature is raised?
A. Density will increase.
B. Density will decrease.
C. Density will remain the same -ANSWER ✔️✔️C. Pressure and temperature
increase by the same ratio
d=pm/RT
A 1.00 L flask contains a mixture of Ar, N2 and
O2. If PTotal = 4.5 atm, and PAr = PO2 = 1.0 atm, what is PN2?
A. 1.0 atm
B. 1.5 atm
C. 2.5 atm
D. Cannot be determined unless
temperature is given -ANSWER ✔️✔️C. Ptotal = PAr + PO2 + PN2
4.5 = 1 + 1 + PN2
PN2 = 2.5
A 1.00 L flask contains a mixture of Ar, N2, and O2.
If PTotal = 4.5 atm, and PAr = PO2 = 1.0 atm, what is the volume occupied by
the oxygen?
,A. 0.22 L
B. 0.56 L
C. 1.00 L
D. Cannot be determined unless
temperature is given -ANSWER ✔️✔️C. Occupies entire flask even when part of
a mixture
Gas Mixtures: Key Concepts -ANSWER ✔️✔️Ptotal = PAr + PO2 + PN2
Pgas = (ngas/ntotal) * Ptotal
ngas/ntotal = Xgas, mole fraction
*a gas that makes up 21% or .21 of a mixture will contribute 21% of the total
pressure*
A 1.00 L flask contains a mixture of Ar, N
2, and O2.
If PTotal = 4.5 atm, and PAr = PO2 = 1.0 atm, what is the mole fraction of Ar?
A. 0.22
B. 0.56
C. 1.00
D. Cannot be determined unless
temperature is given -ANSWER ✔️✔️A. PV = nRT
PAr/Ptotal
1.0/4.5
If more N2 is introduced into the same flask so
that its partial pressure increases to 4.0 atm,
what happens to PO2?
, A. It increases
B. It decreases
C. It stays the same -ANSWER ✔️✔️C. It stays the same
CH4 and O2 are mixed in a stoichiometric
ratio in a glass flask, the total pressure in the
flask is 600 mmHg. What is the partial pressure
of each gas prior to combustion?
To determine the "stoichiometric ratio",
we need a balanced chemical equation.
What is it? -ANSWER ✔️✔️CH4 + 2O2 = CO2 + H2O
CH4 and O2 are mixed in a stoichiometric ratio in a
glass flask, the total pressure in the flask is 600
mmHg. What is the partial pressure of each gas prior
to combustion?
balanced chemical equation is: CH4 + 2O2 = CO2 + H2O
A. PO2 = 600 mmHg PCH4 = 600 mmHg
B. PO2 = 300 mmHg PCH4 = 300 mmHg
C. PO2 = 400 mmHg PCH4 = 200 mmHg
D. PO2 = 450 mmHg PCH4 = 150 mmHg -ANSWER ✔️✔️C. 2:1 mole ratio
between O2 and CH4 = 600
PO2 = 400
PCH4 = 200
The pressure of O2 in a 2.50 L flask is 3.0 atm. When
the stopcock connecting the flask to an empty 1.5 L
