Chemistry, 10.11.2019 14:31, elijahsantiago21

Which of these statements are true? select all that apply.
the hrxn for the reaction c(s) + o2(g) co2(g) is the same as the hf for co2(g). the hrxn for the reaction na(s) + cl2(g) 2nacl(s) is the same as the hf for nacl(s). the hf for br2(l) is 0 kj/mol by definition.
to determine the hf for h2o(g), just reverse the sign of the hrxn for the reaction 2h2o(l) 2h2(g) + o2(g).
the hf for n2(l) is 0 kj/mol by definition.
the hrxn for the reaction 1.5h2(g) + 0.5n2(g) nh3(g) is the same as the hf for nh3(g).

Answers: 2

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In order to find the two statements, we must first define what the enthalpy of formation and the enthalpy of reaction mean.

Enthalpy of formation:
The change in enthalpy when one mole of substance is formed from its constituent elemetns at standard state.

Enthalpy of reaction:
The change in enthalpy when a reaction occurs and the reactants and products are in their standard states.

Now, we check the statements. The true ones are:

The Hrxn for C(s) + O₂(g) → CO₂(g) is the same as Hf for CO₂
This is true because the formation of carbon dioxide requires carbon and oxygen in their standard states.

The Hf for Br₂(l) is 0 kJ/mol by definition.
Because the bromine is present in its standard state, the enthalpy of formation is 0.

The Hrxn for the reaction 1.5H₂(g) + 0.5N₂(g) → NH₃(g) is the same as the Hf for NH₃(g)
The reactants and products are present in their standard state, and the reaction is the same as the one occurring during the formation of ammonia.

answered: elbehairy64

The statements that are true are 1, 3, and 6. The statements are:

The $\rm H_r_x_n$ for the reaction C(s) + $\rm O_2$ (g) $\rightarrow$ $\rm CO_2$ (g) is the same as the $\rm H_f$ for $\rm CO_2$ (g).The $\rm H_f$ for Br2(l) is 0 kJ/mol by definition.The $\rm H_r_x_n$ for the reaction $\rm 1.5\;H_2(g)\;+\;0.5\;N_2(g)\;\rightarrow\;NH_3(g)$ ) is the same as the $\rm H_f$ for $\rm NH_3(g)$ .

The $\rm H_r_x_n$ has been a change in the enthalpy when the reaction takes place. The $\rm H_f$ has been the enthalpy of formation of a product in the reaction.

1. The $\rm H_r_x_n$ for the reaction C(s) + $\rm O_2$ (g) $\rightarrow$ $\rm CO_2$ (g) is the same as the $\rm H_f$ for $\rm CO_2$ (g).

The statement has been true, as the formation of gaseous carbon dioxide requires the carbon and oxygen to be present in their standard existing states.

2. The $\rm H_r_x_n$ for the reaction Na(s) + Cl2(g) 2NaCl(s) is the same as the $\rm H_f$ for NaCl(s).

The reaction has been required with the presence of Cl in the aqueous state, and the formed NaCl will be liquid. Thus, the statement has been false.

3. The $\rm H_f$ for Br2(l) is 0 kJ/mol by definition.

The bromine has been existing in a liquid state in nature, thus the enthalpy of formation of the liquid has been zero. Thus the statement is true.

4. To determine the $\rm H_f$ for $\rm H_2O$ (g), just reverse the sign of the $\rm H_r_x_n$ for the reaction $\rm 2\;H_2O\;(l)\;\rightarrow\;2\;H_2(g)\;+\;O_2(g)$