Enthalphy changes for the following reactions can be determined experimentally:
ID: 976399 • Letter: E
Question
Enthalphy changes for the following reactions can be determined experimentally: N_2(g) + 3 H_2(g) rightarrow 2 NH_3(g) Delta_THdegree = -91.8 kJ/mol-rxn 4NH_3(g) + 3 O_2(g) rightarrow 4 NO(g) + 6 H_2O(g) Delta_THdegree = -906.2 kJ/mol-rxn H_2(g) + 1/2O_2(g) rightarrow H_2O(g) Delta_THdegree = -241.8 kJ/mol-rxn Use these values to determine the enthalpy chance for the formation of NO(g) from the elements (an enthalpy change that cannot be measured directly because the reaction is reactant-favored). 1/2 N_2(g) + 1/2 O_2(g) rightarrow NO(g) Delta_rHdegree = ?Explanation / Answer
divide (1) by 2 so N2 gets 1/2 as coefficeint
1/2N2 + 3/2H2 = NH3 HRxn = -91.8/2 = -45.9
divide (2) by 4, so we cancel NH3 and get NO with 1 coeff
NH4 + 5/4O2 = NO + 3/2H2O HRxn = -906.2/4 = -226.55
multilpy (3) by 3/2 and invert so we can cancel H2O
3/2 H2O = 3/2 H2 + 1/2 O2 HRxn = -241.8*3/2*-1 = +362.7
add all
1/2N2 + 3/2H2 + NH3 + 5/4O2 + 3/2 H2O = NH3 + NO + 3/2H2O+3/2 H2 + 1/2 O2
cancel common terms
HRxn = -45.9 -226.55 + 362.7= 90.25 kJ/mol
cancel common terms
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