What conclusion can be drawn about the number of elements the make up the majority of the world in which we live and the total number of elements identified on the Periodic Table?

Answer

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There are many elements in the universe, However, the universe is 98% hydrogen and hellium and only 2% other elements. This is due to the fact that hydrogen and helium and the easiest to make, it requires little energy. But in the universe, there are many potential elements some of which are not naturally occurring.

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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.