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Math Help - Which of the following statements concerning heat and temperature is FALSE? (Chem)

  1. #1
    s3a
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    Which of the following statements concerning heat and temperature is FALSE? (Chem)

    Which of the following statements concerning heat and temperature is FALSE?
    A) Temperature is simply a way to measure heat.
    B) A substance’s heat content depends on its temperature and total mass.
    C) At the same temperature, identical molecules have the same average kinetic energy.
    D) If air molecules have the same kinetic energy as H2O(g) molecules, the air molecules are on average moving slower than the H2O(g) .

    *The answer is A. Can someone please explain to me A, B, and C? (I understand D)
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  2. #2
    o_O
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    Temperature and heat are not the same thing. Temperature is the measure of average kinetic energy of a given system while heat is its total energy (which is made up of more than its kinetic energy).

    Take boiling water for example. As it reaches 100 degrees Celcius, any heat energy absorbed by water molecules contributes to a change in its potential energy (specifically, the breaking of any intermolecular bonds and whatnot). That is why there is no change in temperature during a phase change as the input energy does not contribute to its kinetic energy. When ice melts into water or when water evaporates, you will not see a change in temperature until the phase change is completed.

    So in a quick summary, an input of heat does not necessarily correspond to an increase in temperature.

    ___________________

    Edit: Didn't see your other questions.

    B) This is where the concept of specific heat capacity comes in. Every substance requires a different amount of heat energy to increase its temperature for a single unit per unit mass. More heat energy is required to increase the temperature of a substance with a high value (such as water) compared to a substance with a lower one. You should be familiar with the equation: Q = mc \Delta T

    C) A temperature is a measure of average kinetic energy. So if two substances are at the same temperature, then their average kinetic energy must be the same.
    Last edited by o_O; December 23rd 2008 at 11:55 PM. Reason: grammar, explanation
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  3. #3
    MHF Contributor arbolis's Avatar
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    Quote Originally Posted by o_O View Post
    Temperature and heat are not the same thing. Temperature is the measure of average kinetic energy of a given system while heat is its total energy (which is made up of more than its kinetic energy).
    Are you sure that heat is the total energy of a system? I believe heat is not a state function, so that we can't say "this system has x J of heat".

    Also I'm a bit confused, in a change of phase of a substance, we can't apply the equation Q=mc \Delta T, right? So that it's not always true... If I remember well I've read in Resnick-Halliday's Fundamentals of Physics that it is an equation that is always true.
    I know how to calculate the heat absorbed by a substance which is changing of phase, using Q=mL where L is the latent heat of the substance. So what happened with Q=mc \Delta T?
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