Question

For which of the following reactions is ΔH∘rxn equal to ΔH∘f of the product(s)?

You do not need to look up any values to answer this question.

Check all that apply.

Check all that apply.

Na(s)+12F2(g)→NaF(s)

SO(g)+12O2(g)→SO2(g)

Na(s)+12F2(l)→NaF(s)

2Na(s)+F2(g)→2NaF(s)

SO3(g)→12O2(g)+SO2(g)

S(s)+O2(g)→SO2(g)

Answer 1

Recall that

Hf = Heat of formation of a specie

HRxn = Hproducts - Hreactants

for formation:

- must be elemental,

- must be standard states

- product must be "pure" and not a compound

so

Na(s)+1/2F2(g)→NaF(s)

CORRECT note that F2(g) is elemental state + Na(s) also

NaF must have a coefficient = 1, this is HF as well!

SO(g)+1/2O2(g)→SO2(g)

Note that reactant must be S(S) and O2(g) so this fails

Na(s)+12F2(l)→NaF(s)

Can't be since F2 elemental / standard state is gas, not liquid

2Na(s)+F2(g)→2NaF(s)

Can't be, since this is for 2 mol of product, i.e. it is twice the Hf

HRxn = 2*Hf

SO3(g)→12O2(g)+SO2(g)

Can't be, since there are two products

S(s)+O2(g)→SO2(g)

True, since S is solid and O2 is gas