Question

a) A mildly restored ‘Knight-Rider’ 1989 Pontiac Trans Am GTA powered by a 5.7 litre V8 can do a quarter mile S from rest in a time t of about 15 seconds. Using distance: S=a t2 /2 , force: F=ma and work: W=FS, calculate the amount of work (energy) in kJ required to do the standing quarter mile given that the mass (m) of this Trans Am is 3,500 pounds. Assume that the acceleration (a) is constant. (This is not actually a good assumption.) You will need to convert lots of units here.  

b)The molecule: iso-octane C8H18 is actually a pretty good representative molecule in petrol. When liquid iso-octane burns in a limited supply of oxygen (as in hard acceleration) it produces carbon monoxide CO and water according to the following unbalanced reaction: C8H18 (l) + O2(g) ? CO (g) + H2O (l) First, balance this equation. Now answer the following: How much heat in kJ is evolved in the burning of one mole of C8H18 to CO? The enthalpies of formation are: ?Hf° (C8H18 (l)) = -208.5 kJ mol-1 , ?Hf° (CO (g)) = -110.6 kJ mol-1 , ?Hf° (H2O (l)) = -284.9 kJ mol-1 . (Check the text to see why you don’t need the enthalpy of oxygen.) Answer (show how you get this answer):

CO can oxidize further to carbon dioxide CO2 according to the following reaction: CO(g) + ½ O2 (g) ? CO2 (g) and the amount of heat evolved for one mole of CO burning to form one mole of CO2 is 284 kJ. Combine the above two chemical equations in order to determine the amount of heat evolved when one mole of C8H18 burns completely to form CO2.  

c) Given that the density of liquid C8H18 is 0.702 g ml-1 at 25°C and the atomic masses of carbon and hydrogen are C = 12g and H = 1g, what is the mass of one litre of liquid C8H18? How many moles of C8H18 are there in one litre of liquid C8H18?

d) Now determine how much petrol in litres were used by the Trans Am to do the standing quarter mile assuming that the engine is only 20% efficient under very rapid acceleration and that combustion of C8H18 was complete to the gas CO2. Hint: from part (a) of this question first calculate how much chemical energy is required to do the acceleration. Now look at your answers in the first part of (b) and also (c) and then determine how many litres you need.

e) How many moles of CO2 were produced in this acceleration?

What is the volume of this CO2 gas at 25°C and atmospheric pressure? (Use the Ideal Gas Equation)

Answer 1

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