Cliffs AP Chemistry, 3rd Edition

Since for every mole of hydrogen produced, one mole of zinc is consumed, the last step would
be to convert these moles to grams by multiplying by the molar mass of zinc.

.

.

/..

11

1

1

65 39

0 0821 313

moles H 665 760 8 00 65 39

mole H

mole Zn

mole Zn

2 gZn

2

::

:

::

=

^

^

h

h

6. What is the partial pressure of helium when 8.0 grams of helium and 16 grams of oxygen
   are in a container with a total pressure of 5.00 atm?

A. 0.25 atm

B. 1.00 atm

C. 1.50 atm

D. 2.00 atm

E. 4.00 atm

Answer: E

Use the formula

P 1 =nntotal^1 Ptotal

derived from Dalton’s law of partial pressures. Find the number of moles of the two gases first.

.

..

gHe

gHe

(^80) mole He moles He
40
(^120)
1 # =
.
gO
gO
mole O mole O
1
16
32
(^21050)
2
#^2 = 2
ntotal= 2.0 moles + 0.50 mole = 2.5 moles
He.
.
P moles ..
moles
25 atm atm
20
==# 500 400

7. For a substance that remains a gas under the conditions listed, deviation from the ideal
   gas law would be most pronounced at

A. − 100 °C and 5.0 atm

B. − 100 °C and 1.0 atm

C. 0 °C and 1.0 atm

D. 100 °C and 1.0 atm

E. 100 °C and 5.0 atm

Answer: A

The van der Waals constant acorrects for the attractive forces between gas molecules. The con-
stant bcorrects for particle volume. The attractive forces between gas molecules become pro-
nounced when the molecules are closer together. Conditions which favor this are low
temperatures (− 100 °C) and high pressures (5.0 atm).

The Gas Laws