1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Specific & Latent Heat

  1. Nov 4, 2011 #1
    1. The problem statement, all variables and given/known data

    How much heat is required to change 1.75 L of Ethyl Alcohol (C2H6O) at -50.0°C to a gas at its boiling point?

    Ethyl Alcohol
    V = 1.75 L
    Ti = -50°C

    46 g/mol
    density = 0.789 g/cm3
    boiling point = 78°C
    specific heat (c)= 2400 J/kg*C°
    Heat of Vaporization (Lv) = 850*103 J/kg

    2. Relevant equations

    density m = ρV

    specific heat Q = mcΔT

    latent heat Q = mLv

    3. The attempt at a solution

    First I determined the mass of the Ethyl Alcohol

    m = ρV = (0.789 g/cm3) (1750 cm3) = 1380.75 g = 1.38075 kg

    Then I solve for QNET

    QNET = (mcΔT)l + mLv

    QNET = [1.38 kg (2400 J/kg*C°) (78°C - (-50°C)] + [1.38 kg (850*103 J/kg)] = 1.60 * 106 J

    According to the answer sheet, the answer is 4.24*105 J
    What am I doing wrong?

    Thank you in advance! Any and all help is appreciated!
  2. jcsd
  3. Nov 4, 2011 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    The answer sheet apparently has only accounted for the heat required to raise the temperature of the liquid ethanol from -50C to 78C.
  4. Nov 4, 2011 #3
    So, did I do it correctly? It did say that "to a gas" . From my understanding of the problem as worded, I have to account for the amount of heat required to bring it to its boiling point, as well as the amount of heat required to turn it into a gas, right? Or did I do it incorrectly and I'm only suppose to calculate the amount of heat needed to bring it to the boiling point?
  5. Nov 4, 2011 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Only your professor knows for sure.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook