Is oxygen an element or a compound? explain.

Element

Oxygen is an element and not a compound.

Elements are substances that can't be split into simpler substances by chemical means. They include, hydrogen, oxygen, sodium, etc.

Compounds are substances that are made up of two or more elements e.g. water is a compound, since it is made up of oxygen and hydrogen element. Compounds unlike elements can be split into simpler substances by chemical means.

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.