Chemistry 30- Molar Enthalpy and Combustion Question HELP!

Question

A 5.00 g sample of nitromethane was burned in a calorimeter that contained 250 g of water at 20.5°C. Calculate the final temperature of the water if all 5.00 g of nitromethane is combusted. Hint - you will need to use the molar enthalpy of combustion. The molar enthalpy of combustion for nitromethane is approximately −354.6 kJ/mol. Write it into appropriate significant digits. Thank you! Appreciate it!

Answer 1

Molar mass of nitromethane (CH₃NO₂) = 61.04 g / mole

moles nitromethane burned = 5.00 g x 1 mol / 61.04 g = 0.0819 moles

Heat generated from burning 0.0819 moles nitromethane = 0.0819 mol x 354.6 kJ/mol = 29.05 kJ (29,050 J)

To find the final temperature of the water, we will use q = mC∆T

q = heat = 29,050 J

m = mass of water = 250 g (assuming a density of 1 g / ml)

C = specific heat of water = 4.184 J/gº

∆T = change in temperature = ? (the temperature will rise from 20.5º to the final temp.)

Solving for ∆T we have...

∆T = q / (m)(C) = 29,050 J / (250 g)(4.184 J/gº)

∆T = 27.8º

Final temperature of the water = 20.5º + 27.8º = 48.3ºC