Enthralpy Question.?

Question

When 0.150 g of liquid octane. C8H18 was burned in a flame calorimeter containing 1.500 kg of water, the temperature of the water rose from 25.246 degrees celsius to 26.386 degrees celsius. What is the standard enthalpy of combustion of octane at 25 degrees celsius?

Answer 1

First calculate the heat gaind by the water

q = m Cp delta T

m = 1500 grams
Cp = 1 cal / g oC
delta T = 26.386-25.246

Now you can calculate the number of calories.

Divide that by 0.150 grams of octane and you have the standard ebthalpy per gram. If you want it per mole, multiply by the molecular mass of octane.