Posted by Hannah 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 A as being incorrect because b and c look correct and the value of delta for c is 4 times the amount of b so I think there are correct. A does not fit in.
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 chose +338.1 as the answer.
3) Consider the following of sulfur trioxide according to the reaction:
2 SO2 (g) + O2 (g) > 2 SO3 (g) deltaH= 198
What is the value of delta H for SO3 (g) > SO2 (g) + 1/2 O2 (g) ?
a) +99
b) 396
c) +396
d) 99
e) some other value
I chose answer a, +99 because the equation is flipped and is half of the original.
Are these answers correct?

chemistry(Please check) 
DrBob222,
I agree with all three answers. Good work.

chemistry(Please check) 
Hannah,
Thank you for checking my work!!!

chemistry(Please check) 
Rick,
Can you explain for the second questions how you got +338.1? Because per my way of doing it 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