Question

Use the data in the table above to calculate an approximate ΔH∘ in kilojoules for the synthesis of hydrazine from ammonia:

2NH3(g)+Cl2(g)⟶N2H4(g)+2HCl(g)
Express your answer to two significant figures and include the appropriate units.

Answer 1

Hi, I just researched for the data since you forgot to present it: These are the standard enthalpies of formation:

NH3(g): -45.9 kJ/mol
N2H4(g): +95.4 kJ/mol
HCl(g): -92.3 kJ/mol

We use Hess's law to find the the deltaH of the reaction.

ΔHrxn = ∑(v × standard heat of formation of products) - ∑(v × standard heat of formation of reactants)

where v is the coefficient found in the balanced reaction. The heat of formation of diatomic molecules is zero. Thus,

ΔHrxn = (+95.4 + 2*-92.3) - (2*-45.9)
ΔHrxn = +2.6 kJ/mol