g A solution containing 3.6 mol of benzene ( C6H6 , b. p. 80°C) and 5.4 mol of toluene (C6H5CH3 , b. p 110°C) is placed in a closed container at 35°C. Some evaporation takes place. What is the mole fraction of toluene in the vapor phase when equilibrium is reached? At 35°C, vapor pressures are: benzene 160. torr, toluene 50.0 torr. HINT: Use Raoult’s Law to find the total vapor pressure, then calculate the fraction of the pressure that is due to toluene vapor. A) 0.52 B) 0.67 C) 0.33 D) 0.14 E) 0.60

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol