The mass of an atom of manganese is 54.9380u how many neutrons are contained in one atom of this elements

- There would be 30 neutrons.

Solution:-  We know that:

atomic mass = protons(mass of 1 proton) + neutrons(mass of 1 neutron)

atomic mass is given as 54.9380 u. Mass of proton is 1.0073 u and mass of neutron is 1.0087 u.

Atomic number for Mn is 25 means it has 25 protons. Let's plug in the values in the formula and calculate the number of neutrons for it.

54.9380 = 25(1.0073) + n(1.0087)

where n is the number of neutrons.

54.9380 = 25.1825 + 1.0087n

54.9380 - 25.1825 = 1.0087n

29.7555 = 1.0087n

n =

n = 29.5

It could be round to 30.

So, there would be 30 neutrons in an atom of Mn.

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.