Question

When urea (CO(NH2)2) (∆Hf

o = -319.2 kJ/mole) reacts with liquid water, the products are

aqueous carbon dioxide and aqueous ammonia.   What is amount of heat (kJ)produced/absorbed when 35.00 g of urea reacts with excess liquid water?

Answer 1

CO(NH₂)₂ + H₂O 2NH₃ + CO₂

Molar mass of CO(NH₂)₂ = 60.06 g/mol

So, 60.06 g of CO(NH₂)₂ = 1 mol

35.00 g of CO(NH₂)₂ = (35.00 / 60.06) mol = 0.583 mol

H_f^o (CO(NH₂)₂) = - 319.2 kJ/mole

1 mole of (CO(NH₂)₂) formation produces = - 319.2 kJ

0.583 mole of (CO(NH₂)₂) formation produces = (0.583) (- 319.2 kJ) = - 186.09 kJ

When the reaction for the formation is identical to the reverse of the reaction for decomposition then the heat of formation of a compound is equal, but of opposite sign for the heat of decomposition.

So, decomposition of urea = + 186.09 kJ.

answered by: anonymous