Ammonia reacts with oxygen to produce nitrogen and water?

- 1276.2 kJ.

Explanation:

ΔHrxn = ∑(n ΔHproducts) - ∑(n ΔHreactants)

∴ ΔHrxn = [(6 x ΔHf H₂O) + (2 x ΔHf N₂)] - [(4 x ΔHf NH₃) + (3 x ΔHf O₂)],

∴ ΔHrxn = [(6 x - 241.8 kJ/mol) + (2 x 0)] - [(4 x -45.9 kJ/mol) + (3 x 0)] = -1450.8 kJ/mol + 183.6 kJ/mol = - 1276.2 kJ.

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