# Homework Help: One gallon of octane is equivalent to 23.4 mol of octane

1. Sep 19, 2010

### grumpyasian

1. The problem statement, all variables and given/known data
one gallon of octane is equivalent to 23.4 mol of octane. the density of it is .703g/mL.

2. Relevant equations

to travel the same distance traveled with one gallon of octane, how many moles of ethanol would you need?( assuming the car works just as well with ethanol as it does with gasoline, same efficiency of conversion of chemical energy to mechanical work.)

3. The attempt at a solution

23.2 mol C8H18(.703g C8H18/mL) (1 mol C2H6O/1 mol C8H18)

idk what to do next

2. Sep 19, 2010

### DDTea

Re: thermodynamics

In a car, chemical energy from gasoline (or in this problem, octane) is being converted to mechanical work. Since we're assuming that both gasoline and ethanol have the same efficiency, we can simply compare the amount of energy per mole that gasoline and ethanol have. Next, you will want to calculate how many moles of ethanol are required to produce the same amount of energy as 23.4 moles of octane (that is, 1 gallon of octane). That will lead you to your answer.

3. Sep 19, 2010

### grumpyasian

Re: thermodynamics

i still don't know what i am still missing in the process of finding the answer. do i times it by 1000mL to cancel out the mL from the density or what? Im totally lost.

4. Sep 19, 2010

### Staff: Mentor

Re: thermodynamics

You need density to convert gallon to mass and moles.