Question

Two moles of SO2 gas are mixed with two moles of O2 gas in a rigid container at constant temperature. The pressure in the container is 8 atm. After the reaction below runs to completion, what will be the new pressure in the container? 2SO2(g) + O2(g) → 2SO3(g)

(1) 1atm (2) 2atm (3) 4atm (4) 6atm (5) 8atm

The answer is 6 atm but I'm not sure why.

Answer 1

reaction taking place is
2SO2(g) + O2(g) → 2SO3(g)
according to reaction
1 mole of O2 required 2 mole of SO2
2 mole of O2 required (2*2) mole of SO2
2 mole of O2 required 4 mole of SO2
but we have only 2 mole of SO2
so,
2 mole of SO2 react with 1 mole of O2
and 1 mole of O2 will remains

again, according to reaction
2 mole of SO2 give 2 mole of SO3
number of mole of SO3 formed = 2 mole

when reaction is completed
total number of mole of gas = (number of mole of SO3 formed)+(number of mole olf O2 remains)
= (2+1) mole
= 3 mole

if 1 denote intial and 2 final
n1 = (number of SO2)+(number of mole of O2)
= 2+2
= 4 mole
use,
P1/n1 = p2/n2
8/4 = P2/3
P2 = 6 atm

Answer : option 4 is correct