Question 1. Calculate The Enthalpy Of Reaction For The - TutorTag

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question 1.

Calculate the enthalpy of reaction for the reaction of nitrogen dioxide with water represented by the following equation:

3 NO2(g) + H2O(l) →2 HNO3(aq) + NO(g) ?rH=?

questiion 2

Nitrogen monoxide gas, which is used to treat some pulmonary diseases, is transported in pressurized gas cylinders. Nitrogen monoxide gas is produced by reacting ammonia gas and oxygen gas, as represented by the following equation. 4 NH3(g) + 5 O2 (g)→ 4 NO(g) + 6 H2O(g)

Calculate the standard enthalpy of reaction for the above equation.

7 years ago

Answered By Leonardo F

This question involves the concept of standard enthalpy of formation. If we multiply the stoichiometric coefficient of each compound in the reaction by its respective standard enthalpy of formation and add for all compounds, we will calculate the enthalpy of the reaction overall. We must remember that we need to add the enthalpy for the products and subtract for the reagents.

In question 1:

From the reference table found in chemistry books:

Standard enthalpy of formation of:

NO2(g) = 33.9 kJ/mol

H2O(l) = -285.8 kJ/mol

HNO3(aq) = -173.2 kJ/mol

NO(g) = 90.4 kJ/mol

Enthalpy of reaction = (90.4)(1) + (-173.2)(2) - (33.9)(3) - (-285.8)(1)

Enthalpy of reaction = -71.9 kJ/mol

In question 2:

Standard enthalpy of formation of:

NH3(g) = -46.2 kJ/mol

O2(g) = 0 kJ/mol

H2O(g) = -241.8 kJ/mol

NO(g) = 90.4 kJ/mol

Enthalpy of reaction = (90.4)(4) + (-241.8)(6) - (-46.2)(4) - (0)(5)

Enthalpy of reaction = -904.4 kJ/mol

The enthalpy of reaction is approximately -904 kJ/mol

PS: Since the temperature of the first reaction wasn't informed, I considered the standard value of 25°C.