Observable matter makes up about what percentage of the universe? 5% 10% 50% 95%

The universe as we know it is home to several galaxies, planets and stars. Hydrogen and helium were the most abundant elements present in the early universe. Heavier elements like carbon, oxygen, phosphorus and even metals were later formed through various fusion reactions in stars.

Nevertheless, matter makes up only 5% of the universe. Nearly 95% is referred to as 'dark matter' which is a subject of research in many scientific communities.

Ans a) 5%

observable matter makes up 5% of the universe

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.