Compare and contrast: element, atom, isotope

Element is made up of the atoms or isotopes. Isotopes are where only neutrons change in number, such as 3 turning to 2 or to 5. Atom is where it is not changed and it is the original, and example is instead of Carbon13 it is just Carbon. I hope this helps.

altitude, density, pressure

air gets less dense the higher the altitude and also the air pressure is less as altitude rises.

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.