Chemistry
posted by Rick on .
1)Which thermochemical equation and data does not agree with the other two written?
a) 2NO (g)+ O2 (g) >2 NO2 (g) deltaH=169.8
b) NO (g) + 1/2 O2 (g) > NO2 (g) delta H = 56.6
c) 4 NO2 (g) > 4 NO (g) + 2 O2 (g) delta H = +226.4
d)all three equations are in thermochemical agreement.
I chose answer D because all seem correct.
2)Calculate the value of delta H for the reaction 2 CH4 (g) > C2H6 (g) + H2 (g) given the following thermochemical equations:
C2H2 (g) + H2 (g) > C2H4 delta H=175.1
C2H6(g) > C2H4 (g) + H2 (g) delta H=+136.4
C2H2 (g) + 3 H2 (g) > 2 CH4 (g) delta H= 376.8
The answer choices are +65.3, +338.1, 415.5, +688.3
I get Delta H as +65.3. Below is how I did it. Please let me know if incorrect.
C2H4 + H2 > C2H6 Delta H = 136.4 (flipped)
2CH4 > C2H2 + 3H2 Delta H = +376.8 (flipped)
C2H2 + H2 > C2H4 Delta H = 175.1

2CH4 > C2H6 + H2 Delta H = +65.3

2 looks ok to me.
1 is not correct. a is the bad one.
Note that c is 4xb but a is not 2xb 
For the problem you worked for Hannah, just a note that it is not necessary to convert to kelvin. Tfinal0Tinitial is the same in degrees C and degrees K since 1 degree C = 1 degree K.
Using kelvin is not wrong; it just takes longer.