Cliffs AP Chemistry, 3rd Edition

Answer: B

Begin by writing down a balanced equation.

2CO(g) + O 2 (g) →2 CO 2 (g)

Next, use the factor-label method to solve the problem.

..
1

22

44

1

2

1

1

gCO 22 4 56

gCO

mole CO

moles CO

mole O

mole O

(^2) LO LO
2
2
2
2
2
###^2 = 2
Hint: Cancel the 22 and the 44 first, leaving 1/4 times 22.4 = 5.61L.

3. If the average velocity of a methane molecule, CH 4 (MW = 16), is 5.00 × 104 cm/sec at
   0 °C, what is the average velocity of helium molecules at the same temperature and
   pressure conditions?

A. 2.50 × 104 cm/sec

B. 5.00 × 104 cm/sec

C. 1.00 × 105 cm/sec

D. 2.00 × 105 cm/sec

E. 5.00 × 105 cm/sec

Answer: C

Graham’s law of effusion:

u

u

MW

MW

2

1

1

=^2

.

x

500 10

16

#^44

=

x= 1.00 × 105 cm/sec

4. When 2.00 grams of a certain volatile liquid is heated, the volume of the resulting vapor
   is 821 mL at a temperature of 127°C at standard pressure. The molecular weight of this
   substance is

A. 20.0 g/mole

B. 40.0 g/mole

C. 80.0 g/mole

D. 120. g/mole

E. 160. g/mole

The Gas Laws