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).

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.

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

The  for the reaction C(s) + (g) (g) is the same as the for (g).The for Br2(l) is 0 kJ/mol by definition.The for the reaction) is the same as the for .

The has been a change in the enthalpy when the reaction takes place. The has been the enthalpy of formation of a product in the reaction.

1. The  for the reaction C(s) + (g) (g) is the same as the for (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 for the reaction Na(s) + Cl2(g) 2NaCl(s) is the same as the 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 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 for (g), just reverse the sign of the for the reaction

The state of hydrogen and oxygen has been different for the formation, thus the statement is false.

5. The for (l) is 0 kJ/mol by definition.

The natural existing state of nitrogen is gaseous. Thus the statement has been false.

6. The for the reaction) is the same as the for .

The statement has been true because of the same states of reactants for the formation of ammonia.

Thus the statements that are true are 1, 3, and 6.

For more information about the enthalpy of formation, refer to the link:

link

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It is a product