Cliffs AP Chemistry, 3rd Edition

Samples: Free-Response Questions

1. Assume that 185.00 grams of fluorine gas and 4.0 moles of xenon gas are contained in a
   flask at 0°C and 2.5 atm of pressure.

(a) Calculate (1) the volume of the flask and (2) the partial pressure of each gas.

(b) 23.00 grams of lithium metal is introduced into the flask, and a violent reaction

occurs in which one of the reactants is entirely consumed. What weight of lithium

fluoride is formed?

(c) Calculate the partial pressures of any gas(es) present after the reaction in part (b) is

complete and the temperature has been brought back to 0°C. (The volumes of solid

reactants and products may be ignored.)

Answer

1. Given: 185.00 F 2 (g) 4.0 moles Xe(g) T= 273K P= 2.5 atm

(a) (1) Restatement: Volume of flask.

PV = nRT

n = total moles = moles F 2 + moles xenon

.

1..

185 00

38 00

moles F gF^1 4 868

gF

2 2 mole F moles F

2

= #^2 = 2

total moles of gas = 4.868 + 4.0 = 8.9 moles

Solve for the volume.

.

..

V nRTP 25

8 9 0 0821 273

mole K atm

moles liter atm K

::

:::

= =

_i

=8.0 × 101 liters

185.00 g F 2

4.0 moles Xe

0 °C

2.5 atm

volume =?

P F 2 =?

P Xe =?

g LiF =?

23.00 g Li

185.00 g F 2

4.0 moles Xe

(violent reaction)

The Gas Laws