W (g) + X (g) - -> Y (g) + Z (g)

Gases W and X react in a closed, rigid vessel to form gases Yand Z according to the equation above. The initial pressure of W (g) is 1.20 atm and that of X (g) is 1.60 atm. No Y (g) or Z (g) isinitially present. The experiment is carried out at constanttemperature. What is the partial pressure of Z (g) when the partialpressure of W (g) has decreased to 1.0 atm?

A) 0.20 atm

B) 0.40 atm

C) 1.0 atm

D) 1.2 atm

E) 1.4 atm

A) 0.20 atm

Explanation:

Let's consider the following reaction.

W (g) + X (g) ⇄ Y (g) + Z (g)

We can find the partial pressure of Z at a time that we will call the equilibrium using an ICE chart. We identify 3 stages: Initial, Change and Equilibrium and complete each row with the pressure or change in pressure.

W (g) + X (g) ⇄ Y (g) + Z (g)

I 1.20 1.60 0 0

C - x - x + x + x

E 1.20 - x 1.60 - x x x

At equilibrium, the partial pressure of W is 1.0 atm.

1.20 atm - x = 1.0 atm

x = 0.20 atm

The pressure of Z is x = 0.20 atm