Question

Be sure to answer all parts. Consider the reaction N2(g) + 3H2(g) → 2NH3(g)

ΔH o rxn = −92.6 kJ/mol

If 4.0 moles of N2 react with 12.0 moles of H2 to form NH3, calculate the work done (in joules) against a pressure of 1.0 atm at 25°C.

?w = (Enter your answer in scientific notation.)

What is ΔU for this reaction? Assume the reaction goes to completion. ΔU = kJ

Answer 1

Be sure to answer all parts. Consider the reaction N2(g) + 3H2(g) → 2NH3(g)

ΔH o rxn = −92.6 kJ/mol

If 4.0 moles of N2 react with 12.0 moles of H2 to form NH3, calculate the work done (in joules) against a pressure of 1.0 atm at 25°C.

Solution :- On the reactant side there are 4+12 = 16 moles of gas

and it produces 8 moles of NH3

so the change in the moles = 16 – 8 = 8

therefore the change in the volume is calculated as

PV = nRT

V= nRT/P

= 8 mol * 0.08206 L atm per mol K * 298 K / 1.0 atm

    = 195.6 L

Now lets calculate the work done

Volume is decreased therefore its -195.6 L

W= - p *delta V

W= - 1atm * (-195.6 L)

W= 195.6 L atm

195.6 L atm * 101.3 J * 1 L atm = 19814 J

So the amount of the work done = 1.9814*10^4 J

What is ΔU for this reaction? Assume the reaction goes to completion. ΔU = kJ

Delta U = q+w

             = (-92.6 kJ*4 mol / 1 mol ) + 1.9814*10^1 kJ

             = -351 kJ