The volume of a gas is 4.0 L, the pressure is 1 atm, and the temperature is 200 K. A chemist changes one factor while keeping another constant so that the new volume is 5.0 L. Which of the following could be the new conditions?

A. The final pressure is 0.8 atm, while temperature is kept constant.

B. The final temperature is 150 K, while pressure remains constant.

C. The final pressure is 1.5 atm, while temperature is kept constant.

D. The final temperature is 100 K, while pressure remains constant.

A. The final pressure is 0.8 atm, while temperature is kept constant.

Explanation:

We can use the general gas law: PV = nRT.

where, P is the pressure of the gas.

V is the volume of the gas.

n is the no. of moles of the gas.

R is the general gas constant.

T is the temperature of the gas.

It is clear that as the volume increase from 4.0 L to 5.0 L, the pressure should decrease (V ∝ 1/P), the temperature should increase (V ∝ T).

So, you can exclude the choices:

B. (T decreases),

C. (P increases),

D. (T decreases).

Thus, the right choice is A, and we can confirm by calculations.

∵ P₁V₁ = P₂V₂.

P₁ = 1.0 atm, V₁ = 4.0 L,

P₂ = ? atm, V₂ = 5.0 L.

∴ P₂ = P₁V₁/V₂ = (1.0 atm) (4.0 L) / (5.0 L) = 0.8 atm.

That's correct, A. The final pressure is 0.8 atm, while temperature is kept constant.