Question

In a piston chamber 15.60 g of Ammonia gas, NH3, is combusted with 34.26 g of oxygen gas producing gaseous water and gaseous Nitric oxide, NO. Consider the Piston chamber to be an ideal isolated system. 4 NH, (g) + 5 O2(g) → 4 NO(g) + 6H2O(g) The pressure in the room is constant at 1.3695 atm and the temperature of the room and chamber are 109.36° C. a. (10 pts) Calculate the heat energy absorbed or released by the combustion of this system. i. Provide a balanced Thermochemical equation for the combustion ii. Determine the molar enthalpy of combustion of ammonia. Use the information below, not the textbook (or internet). Show all work! b. (10 pts) Calculate the work performed by the system, or on the system by the combustion. Use the traditional energy unit to report your value. i Determine initial and final volume of gas(es). Assume that the gases return to room temperature. c. (5 pts) Lastly, what is the change in internal energy? Report in traditional energy units. d. (Very tough! 5 pts) What is the change in temperature of the chamber due to the reaction? Show ALL work.

Answer 1

a.
i. The balanced thermochemical equation for the combustion of ammonia is:

4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(g)

ii. To determine the molar enthalpy of combustion of ammonia, we need to calculate the heat energy absorbed or released by the combustion of the system.

Step-by-step solution:

1. Calculate the moles of NH3 and O2 used in the reaction:
Molar mass of NH3 = 17.03 g/mol
Molar mass of O2 = 32.00 g/mol

Moles of NH3 = 15.60 g / 17.03 g/mol
Moles of O2 = 34.26 g / 32.00 g/mol

2. Determine the limiting reactant:
The limiting reactant is the reactant that is completely consumed in the reaction. It is determined by comparing the moles of reactants to the stoichiometric ratio in the balanced equation.

From the balanced equation, we can see that the stoichiometric ratio between NH3 and O2 is 4:5. Therefore, we need to compare the moles of NH3 and O2 using this ratio.

Moles of NH3 / 4 = Moles of O2 / 5

If the moles of NH3 / 4 is smaller than the moles of O2 / 5, then NH3 is the limiting reactant. Otherwise, O2 is the limiting reactant.

3. Calculate the heat of combustion:
To calculate the heat of combustion, we need to use the enthalpy of formation values for the reactants and products.

Enthalpy of formation (ΔHf) values (in kJ/mol):
NH3(g) = -46.19 kJ/mol
NO(g) = 90.25 kJ/mol
H2O(g) = -241.82 kJ/mol

The enthalpy of combustion (ΔHcomb) can be calculated using the equation:
ΔHcomb = (nΔHf products) - (mΔHf reactants)

Where n and m are the stoichiometric coefficients in the balanced equation.

Calculate the ΔHcomb by using the molar ratios from the balanced equation and the ΔHf values for the products and reactants.

b.
i. To calculate the work performed by the system or on the system by the combustion, we need to determine the initial and final volumes of the gases.

Assuming the gases return to room temperature, the initial and final volumes can be assumed to be the same.

To find the initial and final volumes, we need to use the ideal gas law equation:

PV = nRT

Where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant (0.0821 L·atm/(mol·K)), and T is the temperature in Kelvin.

c.
To calculate the change in internal energy, we can use the first law of thermodynamics, which states that the change in internal energy (ΔU) is equal to the heat transferred (q) minus the work done (w):

ΔU = q - w