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1) That looks right. 2) Step 1: Moles=Mass/Mr, so it's 144/72= 2mol. Step 2: Stoichiometry means the ratio of oxygen to pentane is 1:8 so moles of oxygen is moles of pentane times 8. 2*8=16mol of oxygen. Step 3: 16= 9.6*10^24. 3) The ratio of oxygen to carbon in CO2 is 1:2. so it's 192/3 = 64.
Heat of Combustion. From the previous discussion, we might expect isomers to have identical heats of combustion. However, a few simple measurements will disabuse this belief. Thus, the heat of combustion of pentane is â782 kcal/mole, but that of its 2,2-dimethylpropane (neopentane) isomer is â777 kcal/mole.