4. Why is radiocarbon measurement useless when trying to measure things that died longer than 200,000 years ago?

Radiocarbon measurement or radiocarbon dating is a method that is used to measure the age of the carbon-based material in living organisms.

Radiocarbon dating is able to estimate age of fossils that are younger than 50,000 years and unable to measure things that died longer than 200,000 years ago because fossils that are too old do not contain carbon or carbon get vanished from too old fossils of organisms. Some of the fossils also get contaminated due to environmental conditions and during teh collection or preservation process.

Thus,  radiocarbon measurement is useless when trying to measure most rocks older than 50,000 years.

answer: the enthalpy of the overall chemical reaction is +87.88 kj or +88 kj.

according to hess's law, the overall enthalpy of a reaction is the difference between the sum of enthalpy values of all the products and the sum of enthalpy values of all the reactants.

δh(reaction) = ∑nδh(products) - ∑nδh(reactants)

δh(reaction) = [δh +δh] - [δh]

δh(reaction) = [1(-287.02) + 1(0) ] - [1(-374.9)] kj = +87.88 kj

here, δh (pcl3) = -287.02 kj, δh(cl2) = 0, δh(pcl5) = -374.9 kj

therefore, enthalpy of the overall reaction is +87.88 kj or +88 kj.