C6H14 + 19/2 O2 -> 6 CO2 + 7H2O delta H = -4163 kJ
What mass of hexane is required to produce 1.0E5 kJ of heat by complete combustion?
-4163 kJ/mol x mol C6H14 = 1E5/-4163 kJ/mol
Mol = 1E5/-4163 kJ/mol
Mol = -24 mol
I know I can do m=n x MM now, but shouldn't the value of mol in the above be positive? Or do you just take the absolute value?
In the given chemical equation for the combustion of hexane (C6H14), the value of delta H is -4163 kJ. This value represents the heat released during the combustion reaction.
To calculate the mass of hexane required to produce 1.0E5 kJ of heat, you can use the fact that the delta H value is given per mole of hexane. Here are the steps to follow:
1. Determine the number of moles of hexane required to produce 1.0E5 kJ of heat:
Mol = 1.0E5 kJ / (-4163 kJ/mol)
Mol ≈ -24 mol (rounded to the nearest whole number)
It is important to note that the negative sign in the result implies that the reaction is exothermic, indicating the release of heat. However, in this case, the negative sign does not affect the calculations.
2. Now that we have the number of moles, we can calculate the mass of hexane:
Mass = mol x molar mass of hexane (C6H14)
The molar mass of hexane can be calculated by adding up the atomic masses of its constituents. In this case, carbon (C) has a molar mass of 12.01 g/mol, and hydrogen (H) has a molar mass of 1.008 g/mol.
Molar mass of hexane (C6H14) = (6 x molar mass of carbon) + (14 x molar mass of hydrogen)
= (6 x 12.01 g/mol) + (14 x 1.008 g/mol)
= 72.06 g/mol + 14.112 g/mol
= 86.172 g/mol
3. Substitute the values into the formula to find the mass of hexane:
Mass = -24 mol x 86.172 g/mol
Mass ≈ -2068.13 g or approximately 2068 g
The negative sign in this case doesn't have any physical meaning. So, you can just take the absolute value of the calculated mass, which is approximately 2068 grams. Therefore, approximately 2068 grams of hexane are required to produce 1.0E5 kJ of heat through complete combustion.
The answer is negative because you used a negative number for the kJ/mol. While the negative number is a true representation of an exothermic reaction you are not being consistent. You have two choices:
1. Disregard the negative sign for the -41663 or treat both numbers the same; i.e.,
2. Recognize that the 1E5 kJ you are producing is exothermic, also, and make that a negative number so that dividing a - by a - gives a plus.
As it is you are treating the 4153 as an exothermic reaction (which it is) but you are treating the 1E5 as an endothermic number but the question is asking for the amount of hexane needed to PRODUCE 1E5 (that's exothermic) so you should have a negative sign there too.
Personally, I simply ignore the sign for the 4163 because we know the mols needed must be positive.