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.
5 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.