Calculate ΔH°rxn for 3NO2(g)+1H2O(l) → 2HNO3(g)+1NO(g)

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In summary, to calculate the ΔH°rxn for the given reaction, use the enthalpies of formation for each compound and apply the equation dHrxn = dHproducts - dHreactants. Note that the enthalpy of formation for HNO3 is given as a liquid, so you will need to account for the latent heat using the Hvap of HNO3.
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Homework Statement



Using the enthalpies of formation given below, calculate ΔH°rxn in kJ, for the following reaction.

3NO2(g)+1H2O(l) -> 2HNO3(g)+1NO(g)

NO2 (g): 33.10 kJ/mol
H2O (l): -285.83 kJ/mol
HNO3 (l): -174.10 kJ/mol
NO (g): 90.29 kJ/mol

Homework Equations



dHrxn = dHproducts - dHreactants

The Attempt at a Solution



Is this possible to do since the equation says HNO3 is a gas, but they give the enthalpy of formation for HNO3 as a liquid.
 
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  • #2
its possible but you need to use another enthalpy term that accounts for the latent heat which is from the phase transfer of liquid to gas
 
  • #3
That would be the Hvap of HNO3.
 

1. What is the formula for calculating ΔH°rxn?

The formula for calculating ΔH°rxn is: ΔH°rxn = ΣΔH°f(products) - ΣΔH°f(reactants), where ΔH°f represents the standard enthalpy of formation.

2. How do you determine the enthalpy of formation for each compound?

The enthalpy of formation for each compound can be found in a table of standard thermodynamic data or calculated using Hess's Law and the enthalpy of formation values for elements.

3. What units is ΔH°rxn typically measured in?

ΔH°rxn is typically measured in kilojoules per mole (kJ/mol).

4. Can the ΔH°rxn value be negative?

Yes, the ΔH°rxn value can be negative if the reaction is exothermic, meaning it releases heat energy.

5. How can the ΔH°rxn value be used to predict the spontaneity of a reaction?

The ΔH°rxn value, along with the entropy change (ΔS°) and temperature (T), can be used to calculate the Gibbs free energy change (ΔG°) using the equation ΔG° = ΔH°rxn - TΔS°. If ΔG° is negative, the reaction is spontaneous. If ΔG° is positive, the reaction is non-spontaneous.

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