For which of the following reactions is \Delta H^o_(rxn) equal to \Delta H^o_f of the product(s)? 1. C(s,graphite)+ O_2(g) \rightarrow CO_2(g) 2. Na(s)+12 Cl_2(l) \rightarrow Na…

Question

For which of the following reactions is
`\Delta H^o_(rxn)` equal to
`\Delta H^o_f` of the product(s)?

1.
`C(s,graphite)+ O_2(g) \rightarrow CO_2(g)`
2.
`Na(s)+12 Cl_2(l) \rightarrow NaCl(s)`
3.
`2Na(s)+ Cl_(g) \rightarrow 2NaCl(s)`
4.
`CO(g) + 12O_2(g) \rightarrow CO_2(g)`
5.
`CaCO_3(g) \rightarrow CaO+ CO_2(g)`
6.
`Na(s) + 12Cl_2(g) \rightarrow NaCl(s)`

Answer 1

1 and 6.

Step-by-step explanation:

The enthalpy of reaction (ΔH°rxn) can be calculated by the enthalpy of the formation (H°f) of the components:

ΔH°rxn = ∑n*H°fproducts - ∑n*H°freactants, where n is the number of the moles of the stoichiometric reaction.

So, if ∑n*H°freactants = 0, ΔH°rxn = ∑n*H°fproducts = ΔH°f of the products.

H°f = 0 if the compound is formed by only one element and it is in the ambiental conditions phase. In this case:

H°f of C(s, graphite) = 0

H°f of O₂(g) = 0

H°f of Na(s) = 0

H°f of Cl₂(g) = 0

Thus, it happens only for reactions 1 and 6.