How many moles of argon are in 4.80x10^24 atoms of argon

7.97 mol Ar

Explanation:

Use Avogadro's number to convert atoms to moles.  This number is the number of atoms in one mole.  There are 6.022 × 10²³ atoms in one mole.

Divide the number of atoms given by Avogadro's number.

(4.80 × 10²⁴)/(6.022 × 10²³) = 7.97 mol

There are 7.97 moles of argon.

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.