Cliffs AP Chemistry, 3rd Edition

Step 6: Plug the value for xinto the expression of the equilibrium concentration for NO.

[NO]= 2 x= 2(1.50)= 3.00 M

Note:You could also solve this problemusing equilibrium partial pressures of the gases:

K.

PP

P 400

p NONO

22

2

==

^^hh

Use P = CRT, where C represents the molar concentration of the gas, vn

Try this approach to confirm that [NO] = 3.00 M.

3. Solid carbon reacts with carbon dioxide gas to produce carbon monoxide. At 1,500°C,
   the reaction is found to be at equilibrium with a Kpvalue of 0.50 and a total pressure of
   3.5 atm. What is the proper expression for the partial pressure (in atmospheres) of the
   carbon dioxide?

A.

...

21

-+ 05 0502 - -4 1 35

^

^^^

h

8 hhhB

B.

...

21

-+ 05 0502 - -4 1 175

^

^^^

h

8 hhhB

C.

...

21

-+ 05 050 4 1- - 175

^

^^^

h

8 hhhB

D.

...

21

-+ 05 0502 - 2 1 35

^

^^^

h

8 hhhB

E.

...

21

05 +-- 0502 4 1 175

^

^^^

h

8 hhhB

Answer: B

Step 1: Write the balanced equilibrium equation.

C(s) + CO 2 (g) ↔2 CO(g)

Step 2: Write the equilibrium expression.

P.

P

p^050

CO

CO^2

2

K==

^h

Step 3: Express the two unknowns, pressure of CO and pressure of CO 2 , in terms of a single
unknown, pressure of CO.

Ptotal= PCO+ PCO 2 = 3.5 atm

PCO 2 = 3.5 atm −PCO

Equilibrium