How many grams of CaSO4 (molar mass = 136.2 g/mol) can be produced from the reaction of 0.0126 mol CaBr2 with excess Li2SO4? What is the percent yield if 1.56g CaSO4, is produced?
CaBr2 + Li2SO4 --> CaSO4+ 2LiBr

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