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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: VCE123456789 on October 03, 2010, 03:16:10 pm

Title: Chem Q's
Post by: VCE123456789 on October 03, 2010, 03:16:10 pm: 10 g of heptane is reacted with 10L os O2(g) at 100 degrees celcius in a closed vessel at atmospheric pressure.
Calculate the amount of heat evolved during this reaction?
PLease could anyone help?
Title: Re: Chem Q's
Post by: akira88 on October 03, 2010, 05:03:39 pm: The only way you can do this is knowing the molar enthalpy of heptane, which isn't in the data booklet (it has methane, ethane, propane, butane, pentane, hexane and octane but no heptane...how strange).
However if you had the molar enthalpy of heptane, you would first calculate the amount of mol of heptane and then use ratios to find out the amount of heat evolved:
1: molar enthalpy of heptane
mol of heptane: x
And solve for x (enthalpy*n(heptane))
Title: Re: Chem Q's
Post by: Mao on October 04, 2010, 09:04:17 pm: akira's ratio method is valid, however you must be aware that one of those could be a limiting reagent.

Evaluate n(heptane) and n(O2) using the ideal gas equation with the conditions given. Write the combustion equation and deduce which reactant is limiting, and then calculate the heat of reaction with the change in enthalpy.
Title: Re: Chem Q's
Post by: akira88 on October 04, 2010, 10:17:50 pm: Quote from: Mao on October 04, 2010, 09:04:17 pm
akira's ratio method is valid, however you must be aware that one of those could be a limiting reagent.

Evaluate n(heptane) and n(O2) using the ideal gas equation with the conditions given. Write the combustion equation and deduce which reactant is limiting, and then calculate the heat of reaction with the change in enthalpy.
Oh yes I accidentally assumed heptane was the limiting reactant :(