What is the total pressure in the flask after the temperature returns to 28 degrees C?

Question

A 10.0L flask contains 2.5atm of ethane gas and 8.0atm of oxygen gas at 28 degrees C.

Answer 1

if you are asking for the pressure after you ignited the mix....

2 C2H6 & 7 O2 -->   4 CO2   & 6 H2O

the equation shows it requires 7/2 , ... aka 3.5 times as much oxygen

however they added 8.0 / 2.5 , ... 3.2 times as much oxygen, which is not enough, so oxygen is the limiting reagent

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let's find the pressures produced:

8 atm O2 @ 4 CO2 / 7 O2 =  4.57 atm of CO2 is produced

8 atm O2 @ 6 H2O / 7 O2 =  6.86 atm of H2O is produced

let's find the amount of C2H6 that reacted

8 atm O2 @ 2 C2H6 / 7 O2 = 2.29 atm of C2H6 was used up

let's find how much C2H6 is in excess:

2.5 atm - 2.29 atm = 0.21 atm C2H6 still left over

add up the pressures:

0.21 & 4.57 & 6.86 = 11.64 atm @ end of reaction

your answer is 11.6 atm