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Does anyone know how to do these two questions?

  1. Jun 16, 2004 #1
    Does anyone know how to do these two questions?

    a piece of metal with mass 10 g is heated to a temperature of 60C. when the metal is placed in 50 g water, the temperature of water rises by 22.5 C. what is the specific heat of metal?

    how many moles of KClO3 are needed to form 2.8 L of O2 measured at STP?

    if you noe, plz msg me :P
     
  2. jcsd
  3. Jun 16, 2004 #2

    BobG

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    The overall energy level (in this case, heat) of the two substances combined stays constant. The heat is just redistributed between them, so:

    [tex]m_1 \ast s_1 \ast \Delta t_1 = m_2 \ast s_2 \ast \Delta t_2[/tex]

    (mass times specific heat times change in temperature)

    To solve this, you need to know five of the variables:

    The mass of the metal is given, the mass of the water is given.

    The change in temperature of the water is also given.

    The specific heat of water is most likely given in your book. It's a number that's used often enough you ought to either memorize it or program it as one of your user constants (provided you have a good calculator).

    That gives you four of your variables and you need one more. The original temperature is given and you need the change in temperature. So, you need the final temperature, as well. You haven't been given enough information unless you assume the water started at standard room temperature (25 degrees). This is probably a pretty safe assumption to make if the actual room temperature wasn't given.

    The final temperature of both the metal and the water has to be the same, so the final temperature is just the original temperature of the water plus the change in temperature of the water.

    With that info, you can find the fifth variable and solve for the sixth - the specific heat of the metal. (If it's an elemental metal or a common alloy, you should even be able to determine what the metal is from its specific heat - look in your book or in a chemical handbook).
     
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