Given the following data, what is the enthalpy associated with the reaction? #(i)# #3H_2(g) + O_3(g) rarr 3H_2O(g)#; #DeltaH_"rxn"=??#

#(ii)# #2H_2(g) + O_2(g) rarr 2H_2O(g)#; #DeltaH_1=-483.6*kJ*mol^-1#

#(iii)# #3O_2(g) rarr 2O_3(g)#; #DeltaH_2=284..6*kJ*mol^-1#

1 Answer
Jun 21, 2016

Answer:

Approx. #-100*kJ*mol^-1#

Explanation:

#(i)# #3H_2(g) + O_3(g) rarr 3H_2O(g)#; #DeltaH_?=??#

#(ii)# #2H_2(g) + O_2(g) rarr 2H_2O(g)#; #DeltaH_1=-483.6*kJ*mol^-1#

#(iii)# #3O_2(g) rarr 2O_3(g)#; #DeltaH_2=284..6*kJ*mol^-1#

Treating these algebraically:

#1/2xx(iii)+3/2xx(ii)# #=#

#3H_2(g) +3O_2(g) rarr3H_2O(g) + O_3(g)# #=# #(i)# as required.

And thus #DeltaH_?=3/2DeltaH_2+1/2DeltaH_1#

#(3/2(284.6)+1/2(-483.6))*kJ*mol^-1# #=# #???#

All I have done here is treated each reaction algebraically. In effect, this is a problem with 2 linear equations and 2 unknowns. If I had to reverse the equations, I would have had to reverse the sign on #DeltaH#. Capisce?