Acid rain is a dilute solution of acids that dissolve
the calcium carbonate in limestone statues.
Concentrated acids can dissolve a large piece of
limestone in a few days. Statue breakdown due to
acid rain can take decades, but statues with
intricate carvings break down more quickly.
Explain these observations in terms of reaction
rates.

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