Calculating amount of heat/kJ

Question

Calculate the amount of heat needed to boil 140.g of hexane (C6H14), beginning from a temperature of −37.2°C. Round your answer to 3 significant digits. Also, be sure your answer contains a unit symbol.

Answer 1

Hi Jj N. you'll need a few things: heat capacity of liquid hexane, boiling point of hexane, and heat of vaporization for liquid hexane. The total energy is two parts, first to heat the hexane to the boiling point, and second to get it to actually vaporize. The first part is going to require the heat capacity of liquid hexane, which is in units of energy/amount*temperature (like J/mol*K or J/mol*C). Covert the mass to moles, find the difference in the temperature from boiling hexane to the starting temperature, multiply them all together so the units cross out and you should have the amount of J required to heat the hexane to the boiling point. For the second part the heat of vaporization should just be energy/amount (like J/mol), since the temperature isn't changing. Just multiply them together and moles should cancel out giving you J. Then add the two energy amounts together et voila. Let me know how that goes.