How many neutrons are there in 9 molecules of p4 with mass number 31 and proton number 15?

A = mass number which is equal to the total number of protons + number of neutrons, Z= atomic number of any element which is also indicates Number of protons or number of electron in the given atom.

The formula to calculate neutron would be :

mass number - proton  

31   - 15     = 16

Thus 16 neutrons are found in one atom of P  

There are 4 atom in one molecule

Thus  

4 atom /1 molecule * 9 molecule * 16 neutron / 1 atom  

= 4*9*16= 576 neutrons

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol