Answer:
85.0 kJ
Explanation:
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!!!
