confusing energy reaction question

[lanvins]

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A particular car travels 20000km in a year and operates at a 20% effiency in transforming the chemical energy in fuel into mechanical energy(motion). The car has a fuel consumption of 10L per 100km and its petrol tank holds 50L

a. The amount of energy supplied by a full tank of petrol

b. the amount of energy released as watse heat during the year

[brenton1987]

Originally Posted by lanvins

A particular car travels 20000km in a year and operates at a 20% effiency in transforming the chemical energy in fuel into mechanical energy(motion). The car has a fuel consumption of 10L per 100km and its petrol tank holds 50L
a. The amount of energy supplied by a full tank of petrol

Since petrol is a fairly complicated mixture I'm going to assume that it is 100% octane.

F = 114.2302 g/mol
D = 0.703 g/mL
V = 50000 mL

m = D * V
= 0.703 * 50000
= 35150 g

n = m / F
= 35150 / 114.2302
= 307.7119711 mol

Multiply that by the molar energy of combustion to get the energy of combustion.

[minijumbuk]

Originally Posted by brenton1987

Since petrol is a fairly complicated mixture I'm going to assume that it is 100% octane.

F = 114.2302 g/mol
D = 0.703 g/mL
V = 50000 mL

m = D * V
= 0.703 * 50000
= 35150 g

n = m / F
= 35150 / 114.2302
= 307.7119711 mol

Multiply that by the molar energy of combustion to get the energy of combustion.

But if density wasn't given, wouldn't you have to assume 1L = 1 kg? That's what my teacher told me.

And I thought molar mass had symbol "M"

[brenton1987]

Originally Posted by minijumbuk

But if density wasn't given, wouldn't you have to assume 1L = 1 kg? That's what my teacher told me.

And I thought molar mass had symbol "M"

If it is in an exam situation I guess you could assume 1 L = 1 Kg if it isnt given. If it was not an exam I would expect wider research to be done.

In HS I was always taught molar mass as M or FM for formula mass. Uni usually uses F because 'the no chemistry background tards in first year' get confused with m and M in n = m / M.