How do you use Hess's Law to calculate enthalpy for this reaction?

Given Data:
#"N"_2(g) + "O"_2(g) -> 2"NO"(g)#

#DeltaH = +"180.7 kJ"#

#2"NO"(g) + "O"_2(g) -> 2"NO"_2(g)#

#DeltaH = -"113.1 kJ"#

#2"N"_2"O"(g) -> 2"N"_2(g) + "O"_2(g)#

#DeltaH = -"163.2 kJ"#

Use Hess' Law to calculate #DeltaH# for the reaction:

#"N"_2"O"(g) + "NO"_2(g) -> 3"NO"(g)#

1 Answer
Jose
Mar 31, 2018

#ΔH = 311.3# #"kJ"#

Explanation:

PC of cake

#cancel"N"_2# + #cancel"O"_2# #" ----->"# #2NO#

#2NO_2# #" ----->"# #2NO# + #cancel"O"_2#

#2N_2 O# #" ----->"# #cancel"2"N_2# + #O_2#
#"---------------------------------"#
Adding the 3 equations:

#2NO_2# + #2N_2 O# #" -----> "##4 NO# + # cancel"N"_2# + #cancel"O"_2#

Adding one more reaction
# cancel"N"_2# + #cancel"O"_2# #" -----> "##2 NO#
#"---------------------------------"#
Adding previous 2 equations and dividing by 2

Finally,

#NO_2# + #N_2 O# #" -----> "##3 NO#

The Enthalpy is the sum of the all reactions:

#"=>#180.7 113.1 + (- 163.2) + 180.7 = 311.3 kJ

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