An \"ideal\" fuel/air mixture in which both the fuel and the oxygen in the air a

Question

An "ideal" fuel/air mixture in which both the fuel and the oxygen in the air are completely consumed is called the "stoichiometric" mixture. The stoichiometric mixture is usually specified as the ratio of the mass of air to the mass of a particular fuel. For example, if a fuel (for example, ethanol, C2H;OH) required 9 kg of air to precisely burn 1 kg of the fuel (that is, all the fuel burned and there was no oxygen left in the air afterwards) then the stoichiometric ratio for that fuel would be 9: 1 Calculate the partial pressures of the ethanol and oxygen in the mixture based on the stoichiometric ratio given above at 293.15 K. The volume of the internal combustion engine is considered to be 2.000 L. The mass of the fuel is 400.0 g Mass fraction of oxygen in air is 23.1% Molar mass of ethanol is 46.069 g/mol ethanol atm atm oxygen Submit Answer Try Another Version 4 item attempts remaining

Explanation / Answer

3Mg + N2 ---> Mg3N2

2Mg + O2 ----> 2MgO

Moles of Mg = mass/molar mass = 3.55/24 = 0.148

Now, let x g of MgO is formed and (5.09-x) g of Mg3N2 be formed

Thus, moles of MgO = x/40 and moles of Mg3N2 = (5.09-x)/100

Now, total moles of Mg reacting = 3*moles of Mg3N2 formed + moles of MgO formed

or, 0.148 = (3)*[(5.09-x)/100] + (x/40)

or, x = 0.94 g = mass of MgO

mass of Mg3N2 formed = 4.15 g

2) mass of air required = 9*400 = 3600 g

mass of O2 = 0.231*3600 = 831.6 g

moles of ethanol = mass/molar mass = 400/46.069 = 8.683

moles of O2 = mass/molar mass = 831.6/32 = 25.9875

Total moles of gas mixture = 34.6705

mole fraction of O2 = moles of O2/moles of gas mixture = 0.75

mole fraction of ethanol = 1 - mole fraction of O2 = 0.25

Now, total pressure of gas mixture, P = n*R*T/V = 34.6705*0.082*293.15/2 = 417.23 atm

Thus, partial pressure of ethanol = mole fraction*total pressure = 104.304 atm

partial pressure of O2 = mole fraction*total pressure = 312.914 atm

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.