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Posted: Mon Jan 15, 2018 10:13 pm
For part a, why are we allowed to ignore the 4 moles of C when calculating the heat absorbed in the reaction of 1.25 moles of S8?
Posted: Mon Jan 15, 2018 10:23 pm
It's because we are calculating in terms of S8 moles rather than Carbon (We're calculating using the number of S8 moles rather than C). That means for 1 mole of S8 reacting in the equation, enthalpy change is 358.8 kJ. Our units is thus +358.8 kJ/1 mole S8, which we use to calculate the answer, rather than use the 4 moles of C(s)
Posted: Tue Jan 16, 2018 12:59 pm
If you really wanted to, you can also look at the reaction in terms of carbon, which would be 358.8kj/4mol C. You can then perform stoichiometric conversions to convert moles of S8 to Carbon and whatnot, but because the problem gives the reaction in terms of S8, it would be much more advantageous to look at the calculation in terms of S8.