1. Not finding help here? Sign up for a free 30min 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!

Heat: equal masses of h20

  1. Jun 28, 2003 #1

    Dx

    User Avatar

    Equal masses of water 20C and 80C are mixed. what is the inal temp of the mixture?

    I said 60C
    why is this incorrect?
    Dx
     
  2. jcsd
  3. Jun 28, 2003 #2

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    It's not correct because 60o is the final (not initial) temperature.
     
  4. Jun 28, 2003 #3

    Dx

    User Avatar

    I see
    dx:wink:
     
    Last edited by a moderator: Jun 28, 2003
  5. Jun 28, 2003 #4

    Dx

    User Avatar

     
  6. Jun 29, 2003 #5

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    Once again, DX, be careful of Tom's answers.
    The problem with asking someone to give you the answer is that they may just give you a WRONG answer!

    is not correct. You don't know what the "final" temperature will be because you don't know the temperature of the environment. In order to do this problem, you will have to interpret "initial" temperature as the temperature immediately AFTER mixing.

    What makes you think the temperature will be 60 degrees? The only way I see that you can get 60 is to subtract 20 from 80. Do you have any reason for that? If the two temperatures had been 60 and 50 would you say that the mixture will be 10 degrees? Does that even make sense?

    It should make sense to you that if you mix two things the final temperature will be BETWEEN the two original ones. In fact you should think about finding the average of the two temperatures.
    What is the average of 20 and 80 degrees?

    You should also think about how you would "average" the temperatures there were more water at one temperature than the other.

    Suppose you had 10 grams of water at 20 degrees and 40 grams of water at 80 degrees. ABOUT what do you think the temperature of the mixture would be? How would you calculate it exactly?
     
  7. Jun 29, 2003 #6

    Dx

    User Avatar

    Let me see. 20 + 80 = 100 / 2 = 50 average. I think i understand better now Ivy. Thanks! Can I add you as a friend, plz? Let me try to work the problem further and if I jave anumore problems ill ask.
    Dx :wink:
     
  8. Jun 30, 2003 #7

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Actually, I assumed he did average them and that's how he got 60o. I didn't even notice that 60 isn't the average!
     
  9. Jun 30, 2003 #8

    Dx

    User Avatar

    we forgive you this time Tom.
    Just teasing, i am glad to see that everyone has each others back. Thanks HallsOfIvy,
    I appreciate your help and toms too.
    Dx:wink:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?