Chemistry related question

Question

The density of a gas is 1.96 g L-1 at 1.00 atm and 0 °C. What is the density of this gas at 0.855 atm and 25.0 C?

(A)0.00276 g•L-1

(B)0.651 g:L-1

(C) 1.54 g.L-1

(D) 1.82 g.L-1

Answer 1

(C) 1.54 g.L^-1

The moles of gas will be constant. Only pressure and volume change. The change in volume will affect the density since density is mass / volume. How does the volume change?

V proportional to T/P

@1 atm and 0ºC: V = T/P when moles are constant = 273 / 1 atm = 273

@ 0.855 atm and 25º: V = 298 / 0.855 = 348.5

volume increases by 348.5 / 273 = 1.28 times

Increase in volume = decrease in density

Density = 1.96 g L^-1 / 1.28 = 1.53 g L^-1

If you want to do it the long way, you can use the ideal gas law, PV = nRT and assume an initial volume of 1 L, and solve for n (moles of gas). Then plug that # moles back into the ideal gas law and solve for the new volume at 0.855 atm and 298K.