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    Out of the three following Intermolecular forces, whats the order of strength?
    -Electronegativity (permanent polar dipole-dipole)
    -Van der Waals',
    -Hydrogen Bonds
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    (Original post by S.Ahmad)
    Out of the three following Intermolecular forces, whats the order of strength?
    -Electronegativity (permanent polar dipole-dipole)
    -Van der Waals',
    -Hydrogen Bonds
    Hydrogen bonds>dipole dipole>van der waals

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    (Original post by Diligence)
    Hi,

    I would appreciate it if someone could explain to me why some salts are soluble in water while others such as lithium fluoride are not?

    Thanks
    the enthalpy of solution is positive and too endothermic, this means that there is a the entropy of the surroundings is negative, so despite the entropy of the stystem being postive, the total entropy of the system will be negative.
    Basically, for AS, the ionic bonds are too strong lol
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    Hey please can someone help on this question.. I just don't understand or enthalpy changes of combustion in general or of anything. Like when you do energy released and then switch over and do the opposite sign for temp released.. well all that makes no sense to me. Pls help!


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    http://filestore.aqa.org.uk/subjects...2-QP-JUN12.PDF

    Quesiton 2C. Can someone explain this to me. If the delta h is positive does that mean the reaction is endothermic. How do you know the reaction is to the right is my question basically.

    If it was negative how would you know which way was exothermic or endothermic.

    Is the way you do it by looking at the sign and saying the reaction to the right if negative = endothermic. If delta h is positive reaction to right = endothermic?

    Thanks.
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    Also just tried doing it and got for bi) +56430 but I'm unsure whether it should be negative or not. For bii) 0.02 and for biii) 2820000 but that number seems so big so seems wrong
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    (Original post by zara1234567)
    Hey please can someone help on this question.. I just don't understand or enthalpy changes of combustion in general or of anything. Like when you do energy released and then switch over and do the opposite sign for temp released.. well all that makes no sense to me. Pls help!


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    First question is Q=mcAT. m is the mass of water, c is the specific heat capacity, delta T is the temperature change.

    For second question divide the mass used by molar mass.

    For third use the values above and calculate delta H.
    deltaH=-Q/n

    P.S don't forget to convert to kJ
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    (Original post by zara1234567)
    Also just tried doing it and got for bi) +56430 but I'm unsure whether it should be negative or not. For bii) 0.02 and for biii) 2820000 but that number seems so big so seems wrong
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    Divide by thousand to get kJ/mol
    First question is positive. Third question is negative

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    (Original post by Super199)
    http://filestore.aqa.org.uk/subjects...2-QP-JUN12.PDF

    Quesiton 2C. Can someone explain this to me. If the delta h is positive does that mean the reaction is endothermic. How do you know the reaction is to the right is my question basically.

    If it was negative how would you know which way was exothermic or endothermic.

    Is the way you do it by looking at the sign and saying the reaction to the right if negative = endothermic. If delta h is positive reaction to right = endothermic?

    Thanks.
    The equilibrium will shift to the right therefore the yield will increase.
    According to le Chatelier's principle equilibrium will shift to the way to counteract the disturbance in the system.
    In this case, temperature is increased, so to counter this change endothermic forward reaction will be favoured, resulting in shift of equilibrium to the right.

    In this question forward reaction is endothermic because positive delta H. When there is an equation and delta H next to it, you can assume it is referring to the forward reaction.
    Bond forming is usually exothermic and bond breaking is usually endothermic as well. In this reaction forward reaction is bond breaking so you can also assume it is endothermic that way, although there are some exceptions.

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    (Original post by Super199)
    http://filestore.aqa.org.uk/subjects...2-QP-JUN12.PDF

    Quesiton 2C. Can someone explain this to me. If the delta h is positive does that mean the reaction is endothermic. How do you know the reaction is to the right is my question basically.

    If it was negative how would you know which way was exothermic or endothermic.

    Is the way you do it by looking at the sign and saying the reaction to the right if negative = endothermic. If delta h is positive reaction to right = endothermic?

    Thanks.
    CH4(g) + H2O(g) CO(g) + 3H2(g) ΔH = +206 kJ mol–1

    Yes. If you have positive ΔH value then that means the forward reaction is endothermic and the reverse direction must be exothermic.

    If you have a negative ΔH value then the forward reaction is exothermic and the reverse reaction is endothermic.

    To increase temperature in an equilibrium reaction you must always shift the equilibrium in the endothermic direction. So in your question it would be the right side. This is to absorb the heat, to oppose the increase in temperature. This obeys Le Chatelier's Principle.

    Le Chatelier's Principle:
    "If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change."

    I hope that helps
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    (Original post by C0balt)
    Divide by thousand to get kJ/mol
    First question is positive. Third question is negative

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    Yeah I hadn't divided 1000 to get kj mol. Thank you and whoever else answered for your help 😌

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    http://gyazo.com/845ea9e4cb5ba5f9f4cabfdaa667a45b

    Can someone explain this to me please?
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    (Original post by BBeyond)
    http://gyazo.com/845ea9e4cb5ba5f9f4cabfdaa667a45b

    Can someone explain this to me please?


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    Hope this helps.Oh for the second picture,the line between the carbons is the sigma bond.
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    (Original post by Kadak)
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    Hope this helps
    That makes a lot more sense now, thank you!
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    (Original post by Disney0702)
    CH4(g) + H2O(g) CO(g) + 3H2(g) ΔH = +206 kJ mol–1Yes. If you have positive ΔH value then that means the forward reaction is endothermic and the reverse direction must be exothermic. If you have a negative ΔH value then the forward reaction is exothermic and the reverse reaction is endothermic. To increase temperature in an equilibrium reaction you must always shift the equilibrium in the endothermic direction. So in your question it would be the right side. This is to absorb the heat, to oppose the increase in temperature. This obeys Le Chatelier's Principle. Le Chatelier's Principle: "If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change."I hope that helps
    (Original post by C0balt)
    The equilibrium will shift to the right therefore the yield will increase.According to le Chatelier's principle equilibrium will shift to the way to counteract the disturbance in the system.In this case, temperature is increased, so to counter this change endothermic forward reaction will be favoured, resulting in shift of equilibrium to the right.In this question forward reaction is endothermic because positive delta H. When there is an equation and delta H next to it, you can assume it is referring to the forward reaction.Bond forming is usually exothermic and bond breaking is usually endothermic as well. In this reaction forward reaction is bond breaking so you can also assume it is endothermic that way, although there are some exceptions.Posted from TSR Mobile
    That clears things up. Thank you
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    Anyone do as edexcel biology?? Pm me, need to ask a question

    ...probably not a good place to start on a chemistry thread but oh well


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    Anyone doing F332 and F331:
    Do you have any predications what may come up in the exams and what questions may be asked regarding the pre-release article??
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    (Original post by Elhamm)
    Anyone doing F332 and F331o you have any predications what may come up in the exams and what questions may be asked regarding the pre-release article??
    ah this old chestnut, why not just learn and understand the content instead of trying to predict what will come up?
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    (Original post by langlitz)
    ah this old chestnut, why not just learn and understand the content instead of trying to predict what will come up?
    I have lol, I'm just asking out of curiosity
    Do you do OCR salters??
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    (Original post by Elhamm)
    I have lol, I'm just asking out of curiosity
    Do you do OCR salters??

    Then you shouldn't worry about what comes up, if you understand it you will be able to apply it to whatever they ask you

    No I don't do OCR
 
 
 
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