Calculate the amount of heat needed to melt 160. g of solid octane (C8H18 ) and bring it to a temperature of 99.2 degrees c. Round your answer to 3 significant digits. Also, be sure your answer contains a unit symbol.

To melt 160 g of octane and bring it's temperature to 99.2°C

(from literature)

Heat of fusion of Octane = 20.740 kJ/mol

Melting point of octane = -57°C

Boiling point of Octane = 125.6 °C

Molar mass of octane = 114.23 g/mol

Heat capacity of octane = 255.68 J/K.mol

So, it is evident that Octane is still a liquid at 99.2°C.

So, the required heat is the heat required to melt octane and raise the temperature of Octane liquid to 99.2°C

First, we convert the mass of octane given to number of moles as the heat parameters provided by literature are given in molar units.

Number of moles = (mass)/(Molar mass)

Number of moles of octane = (160/114.23) = 1.401 moles

Heat required to melt the octane = nL = (1.401×20.740) = 29.05674 kJ

Heat required to raise the temperature of already melted octane from its melting temperature of -57°C to 99.2°C

= nCΔT

n = 1.401 moles

C = 255.68 J/K.mol

ΔT = (99.2 - (-57)) = 156.2°C (same as a temperature difference of 156.2 K)

Heat required to raise the temperature of already melted octane from -57°C to 99.2°C

= (1.401×255.68×156.2)

= 55,952.04 J = 55.952 kJ

Total heat required to melt the 160 g of Octane and raise its temperature to 99.2°C

= 29.05674 + 55.952 = 85.01 kJ = 85.0 kJ

Hope this Helps!!!

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2 years ago