T-Mobile 11:27 AM K Chem 131 Practice Exam 5.docx 1 s. A sample of 53.7 grams of

Question

T-Mobile 11:27 AM K Chem 131 Practice Exam 5.docx 1 s. A sample of 53.7 grams of octane C,HIR) burns in a sealed container filled with enough oxygen to give CO and HO. (20 points) Write the balanced equation for the combustion of octane: b.How many moles of octane are in the sample? How many grams of Oxygen (O,) are needed to support the complete reaction? e. What is the mole fraction of CO, and HO at the completion of the reaction? d What is the partial pressure of each product at the end of the reaction if the mixture is brought to a pressure of 6.78 atmospheres? (assume the water remains in the gas phase). Courses Calendar To Do Notifications Inbox

Explanation / Answer

(a)

The balanced equation for combustion of octane is:

C8H18 + 12.5O2 ---> 8CO2 + 9H2O

(b)

Moles of octane = Mass/MW = 53.7/114 = 0.471

So,

Moles of O2 needed = 12.5*0.471 = 5.887

So,

Mass of O2 needed = Moles*MW = 5.887*32 = 188.384 g

(c)

At the completion of reaction:

Moles of CO2 = 8*0.471 = 3.77

Moles of H2O = 9*0.471 = 4.24

So,

Mole fraction of CO2 = XCO2 = 3.77/(3.77+4.24) = 0.47

Mole fraction of H2O = 1-XCO2 = 0.53

(d)

Given:

pT = 6.78 atm

So,

Partial pressure of CO2 = pCO2 = pT*XCO2 = 6.78*0.47 = 3.187 atm

Partial pressure of H2O = pT - pCO2 = 6.78-3.187 = 3.593 atm

Hope this helps !

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