A chemist has 4.0 L of H2 gas at 101.3 kPa and 127°C. How many moles of
H2 does she have?

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

Explanation:

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.

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.