Question

explain Hess's law and give an example :/

Answer 1

water! solid water heats up and begins to melt, melts and you have liquid water which you heat and it begins to boil after it evaporates you have steam, now enthalpy of every that step can be calculated separate and then summed up or it can be calculated as one transition

Answer 2

what do you mean by 1 transition? o.0

Answer 3

solid -> liquid -> gas and solid -> gas (sublimation)

Answer 4

um can you give me a example problem?

Answer 5

calculate total enthalpy of water transitions s->l->g and compare your results to total enthalpy calculated by sublimation of water s->g(results must be the same!!!)

Answer 6

don't i need the amount of water?

Answer 7

here is one other example:
B2O3 (s) + 3H2O (g) → 3O2 (g) + B2H6 (g) (ΔH = 2035 kJ/mol)
H2O (l) → H2O (g) (ΔH = 44 kJ/mol)
H2 (g) + (1/2)O2 (g) → H2O (l) (ΔH = -286 kJ/mol)
2B (s) + 3H2 (g) → B2H6 (g) (ΔH = 36 kJ/mol)

Find the ΔHf of:

2B (s) + (3/2) O2 (g) → B2O3 (s)

Answer 8

in this website, the guy explains each step. I think it's easier to understand.
http://www.chemteam.info/Thermochem/HessLawIntro1.html

Answer 9

H2O (l) → H2O (g) (ΔH = 44 kJ/mol)
qvaporization=18.02g x 44kj/mol ?
did i do it right?

Answer 10

no here is the point that you can turn equations around but must change foretoken of the enthalpy, by which i mean you can turn that equation above from product to reactants and change foretoken of enthalpy, its a bit hard to explain it like this better consult a book or pigrenex-es link

Answer 11

can you show me how to do H2O (l) → H2O (g) (ΔH = 44 kJ/mol)?

Answer 12

better look at pigrenex-es link and follow what is there written so you understand it...