Question

Which equation has a ΔHrxn that is not equal to ΔHof of the product?

Select one:

a. O2(g) + H2(g) → H2O2(g)

b. ½O2(g) + H2(g) → H2O(g)

c. H2(g) + ½O2(g) + → H2O(l)

d. NO(g) + ½O2(g) → NO2(l)

e. ½H2(g) + ½Cl2(g) → HCl(g)

Answer 1

for delta Horxn to be delta Hof,

rule 1: there must be only 1 mol of product being formed

rule 2: reactant must be element in there standard state

a)

This satisfies both rule

So, ΔHrxn is equal to ΔHof

b)

This satisfies both rule

So, ΔHrxn is equal to ΔHof

c)

This satisfies both rule

So, ΔHrxn is equal to ΔHof

d)

NO is compound in reactant side.

rule 2 fails

So, ΔHrxn is not equal to ΔHof

e)

This satisfies both rule

So, ΔHrxn is equal to ΔHof

Answer: d