2,2-dimethylhexane has a heat of formation of -186.9kJ/mol.

Question

2,2-dimethylhexane has a heat of formation of -186.9kJ/mol. Assuming an isolated system that uses this substance as a fuel, what mass of the substance would be required to heat 335g of water from 21.0°C to 62.5°C?

Answer 1

First, let us determine the amount of heat needed to raise the temperature of 335 g water from 21.0º to 62.5º. For this, we will use q = mC∆T...

q = heat = ?

m = mass of water = 335 g

C = specific heat of water = 4.184 J/gº

∆T = change in temperature = 62.5º - 21.0º = 41.5º

q = (335 g)(4.184 J/gº)(41.5º)= 58168 J = 58.17 kJ

Next, knowing that 2,2 dimethylhexane has a heat of formation of -186.9 kJ/mol, we can determine how many moles it will take to provide 58.17 kJ of heat determined above.

58.17 kJ x 1 mol /186.9 kJ = 0.311 moles of 2,2 dimethylhexane

To convert this to grams, use the molar mass of 2,2 dimethylhexane (114 g / mol)

0.311 mols x 114 g / mol = 35.4 g 2,2 dimethylhexane needed