Question

@aaronq @sagnik_das

Use Hess's law and the following equations to calculate ΔH for the reaction SO2(g) + NO2(g) SO3(g) + NO(g). (Show your work.)

SO3(g) SO2(g) + O2(g) ΔH = –98.4 kJ/mol
N2(g) + O2(g) NO(g) ΔH = 90.3 kJ/mol
NO2(g) N2(g) + O2(g) ΔH = –33.1 kJ/mol

Answer 1

What you're basically doing is cancelling out the \(O_2(g)\) and writing one big equation and adding the \(\Delta\)H

Answer 2

how? @abb0t do i add all the numbers?

Answer 3

you have to arrange (reverse or multiply) the equations at the bottom so when you put them all together it looks the equation at the top. When you reverse an equation, you reverse the sign of the enthalpy. Then just add the values together as it is.

Answer 4

thats still confusing

Answer 5

@aaronq

Answer 6

you wanna arrange these equations:

(1) SO3(g) <-> SO2(g) + O2(g) ΔH = –98.4 kJ/mol
(2) N2(g) + O2(g) <-> NO(g) ΔH = 90.3 kJ/mol
(3) NO2(g) <-> N2(g) + O2(g) ΔH = –33.1 kJ/mol

i numbered them so i can refer back to them.

so they look like this
SO2(g) + NO2(g) <-> SO3(g) + NO(g).

i'll start, for example, look at equation (1), SO2 is on the wrong side, so reverse it, and reverse the dH sign as well:

(1) SO2(g) + O2(g) <-> SO3(g) ΔH = +98.4 kJ/mol


sounds better?