What did sewage treatment in Ancient Rome and 19th century London have in common? How effective was this strategy and why? Why is human waste hazardous when it enters the water system?
Where does the material that enters a septic system end up and why?
What is now done to wastewater that was not done until more recently?
In what way are the two ways of treating sewage really just ways of recycling?

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