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Math Help - Chem help: entropy and enthalpy?

  1. #1
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    Chem help: entropy and enthalpy?

    I missed a few classes and am totally lost for this lab. I have to determine whether or not ammonium chloride dissolving into water is a spontaneous process. I know the answer is yes, but I would much rather know why that is so... I know there is an increase in entropy as a rigid, structured salt is broken down into an aqueous solution. I also know there is an increase in enthalpy as it is an endothermic reaction. I don't know what the driving force is though, is it entropy or enthalpy?

    Also, I need to know whether or not calcium chloride is a spontaneous process. Again, I think the answer is yes, but don't know why. I know that the exothermic qualities of the reaction mean that enthalpy decreases, while entropy increases as the CaCl2 dissociates. I don't know what the driving force here is either.

    Thanks in advance! Would really love some help.
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  2. #2
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    Re: Chem help: entropy and enthalpy?

    Entropy and enthalpy are both driving forces.
    However, since pressure is assumed to be constant, it's best modeled by enthalpy.
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    Re: Chem help: entropy and enthalpy?

    Is this so for all reactions, including calcium chloride? Enthalpy is positive for ammonium chloride, but negative for calcium chloride, would that not make the driving force different for the respective reactions?

    Would the dissolving of sodium chloride also have enthalpy as the driving force? I'm assuming the answer is yes.
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    Re: Chem help: entropy and enthalpy?

    How can I tell from looking at a reaction what the driving force is, or is it always enthalpy when pressure is constant?
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    Re: Chem help: entropy and enthalpy?

    The actual driving force is the electro negativity of the elements involved.
    When ionizing, some elements have a positive enthalpy change and some a negative change.

    When pressure is constant, which is the case for most chemical reactions, we usually look at the enthalpy change.
    If for instance pressure would not be constant, but volume would be constant, we would look at the change in internal energy.
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