chemistry

• Angelababy

  27 Jun 09, 11:01

  A fuel oil contains 87% carbon (C), 11% hydrogen (H) and the rest sulphur (S).  The oil is completely burned with 20% excess air.  Upon complete combustion, carbon is converted to carbon dioxide (CO₂), hydrogen to water (H₂O) and sulphur to sulphur dioxide (SO₂).  All the percentages are by mole.

   

  (a)                    Write three separate balanced chemical reaction equations for the complete combustion of C, H and S respectively.                   (3 marks)

   

  (b)                    Clearly state the basis for this calculation.                                  (1 mark)

   

  (c)                     Calculate the molar composition of the product stream.        (11 marks)

   

  can someone help? i am stucked.

• Angelababy

  27 Jun 09, 11:39

  hmmm...i still cant solve it=(

  answers :

  b) 100 gmol

         c) CO₂ = 16.51%

             H₂O = 1.04%

             SO₂ = 0.38%

             O₂ = 3.48%

             N₂ = 78.59%

   

   

• UltimaOnline

  27 Jun 09, 22:36

  Here's a reply for Angelababy.

   

  The question and/or solution given is flawed (in which course and from which institution did you encounter this question?). Nitrogen for instance, is inert and hence does not qualify as part of the 'product stream'. Assuming the answer given, is what is required by the question, then the question should be rephrased slightly to include molar composition of the residual environmental gas, not merely of the 'product stream'. 20% "excess air" refers to 120% air provided in the combustion chamber, where 100% refers to the air supplying the exact amount of oxygen required for complete combustion of the compound. You can google/wikipedia the average gaseous composition of air.

• Angelababy

  27 Jun 09, 23:36

  thankyou i think i have an idea on how to solve it.

• Angelababy

  27 Jun 09, 23:47

  hmm one more question,when i write the chemical equation for hydrogen react with oxygen.its H react with O2 or H2 react with O2.and when is the time to use H or H2?

• marcteng

  27 Jun 09, 23:55

  wah why the questions are so difficult ones lol you sure its primary school, not university?
• Angelababy

  27 Jun 09, 23:57

   busted.

• UltimaOnline

  28 Jun 09, 00:00

  Originally posted by Angelababy:

  hmm one more question,when i write the chemical equation for hydrogen react with oxygen.its H react with O2 or H2 react with O2.and when is the time to use H or H2?

   

  It should actually be CxHyOz + ___ O2 ---> ___ CO2 + ___ H2O.

   

  Only when you are combusting molecular hydrogen gas, do you use H2, ie.  2H2 + O2 ---> 2H2O

  
  The equation using atomic H, ie.  4H + O2 --> 2H2O is not meaningful or useful in the practical sense.