calculate ΔH for each of the following reactions, which occur on the atmosphere?

Question

1. C2H4(g) + O3(g) -> CH3CHO(g) + O2
in KJ

2. O3(g) + NO(g)-> NO2 (g) + O2(g)
in KJ

3. SO3(g) + H2O(l) -> H2SO4(aq)
in KJ

4. 2NO(g) + O2(g)-> 2NO2(g)
inKJ

Answer 1

Jenny is right. The elements in their standard states are like "sea level", in my other answer. Remember to score elements in standard state as zero, multiply by number of moles in eq., add up products and subtract reactants.

Answer 2

You have to use Hess's Law which says that the ΔH for the reaction is that of the products minus the reactants. you can look up the individual ΔHs from NIST webbook. I'll use #1 as an example.

C2H4(g) + O3(g) -> CH3CHO(g) + O2

C2H4=52.47 kJ/mol
O3= 142.67 kj/mol
CH3CHO=-170.7kJ/mol
O2= 0kJ/mol

(-170.7+ 0) - (52.47+142.67) = 365.84 kJ/mol