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    does anyone have a good structure for answering equilibrium questions for AQA CHEM2??
    Like I understand the topic but I struggle to pick up marks in my answers
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    For the energetic topic(aqa), is there an equation for standard enthalpy of reaction or standard enthalpy of neutralisation?

    And are these equations correct - standard enthalpy of formation H=E(products) - E(reactants)
    Standard enthalpy of combustion - H=E(reactants) - E(products)
    Mean bond enthalpy H=E(bonds broken) - (bonds formed)
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    (Original post by sophiegashman)
    does anyone have a good structure for answering equilibrium questions for AQA CHEM2??
    Like I understand the topic but I struggle to pick up marks in my answers
    eg, If temperature was increased the position of equilibrium will shift to oppose this change and move in the endothermic direction to try and reduce the temperature by absorbing heat
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    (Original post by Fishhy34)
    I need help I do OCR salters B and its a question about Nucleophiles
    I was wondering whether in all nucleophilic substitutions whether reflex is required and heating it under NaOH or is it only when a hydroxide substitutes the halogenoalkane.

    Thanks
    HO- Neucleophile need reflux/heat + NaOH(I think the NaOH therefore provides the neucleophile as ions would probably be independent if aqueous).also ethanol solvent
    Water needs to be heated under reflux
    NH3 needs heat in sealed tube with concentrated ammonia
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    Is hydration of alkenes nucleophillic addition?

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    (Original post by Isabella~)
    Is hydration of alkenes nucleophillic addition?

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    Electrophilic
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    (Original post by TeachChemistry)
    Electrophilic


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    How come, isn't water a nucleophile?
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    It can be as it can donate a lone pair but it can also be polarised when approaching Alkene double bond(high negative density because 4 e-) and a species with a + or partially +ve region is a electrophile

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    (Original post by Isabella~)
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    How come, isn't water a nucleophile?
    It can be as it can donate a lone pair but it can also be polarised when approaching Alkene double bond(high negative density because 4 e-)
    and a species with a + or partially +ve region is a electrophile

    My mistake the hydrogen is already partially polarised(no need for polarisation) due to difference in electronegativity. It's still attracted to double bond hence water is a electrophile
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    (Original post by Isabella~)
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    How come, isn't water a nucleophile?
    If you review the mechanism for reaction with water you will see the first step is reaction of the double bond with an H on the water. By virtue of electronegativity difference between O and H, the H is delta positive. The mechanism is described as electrophilic addition.
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    *URGENT ANSWER NEEDED PLEASE*

    For anyone that did the chemistry unit 1 Edexcel test last friday, can someone please tell me if, for the question where we had to identify the errors on the drawing of the mechanism, we were supposed to JUST identify the errors or identify the errors AND state how they would be corrected? The question was 3 marks but I'm doing this unit 2 paper from last year with a similar question also worth 3 marks but we have to say how to correct it as well for this one so I'm kinda worried :/

    THANK YOU
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    hey, im doing OCR AS Chemistry A, and i was wondering if anyone could help me out
    im struggling to understand catalytic converters:confused: i was away for the lesson and the sheets the teacher gave me dont really make any sense,
    thank you, kirsten
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    (Original post by _kirstxn)
    hey, im doing OCR AS Chemistry A, and i was wondering if anyone could help me out
    im struggling to understand catalytic converters:confused: i was away for the lesson and the sheets the teacher gave me dont really make any sense,
    thank you, kirsten
    There's not much to know here. Look at textbook p.231 and specification p. 36. What do you not understand in particular?
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    Hey I am doing OCR AS can anyone tell me the mechanisms i need to know for unit 2?
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    (Original post by AH5223)
    Hey I am doing OCR AS can anyone tell me the mechanisms i need to know for unit 2?
    Electrophilic addition
    Nucleophilic substitution
    Free radical substitution
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    (Original post by TeachChemistry)
    There's not much to know here. Look at textbook p.231 and specification p. 36. What do you not understand in particular?
    theres a question in the textbook on p.231 "How are harmful Nox and CO formed in a car engine?" i feel like i know the basics of the information but im a bit 'iffy' on how to go about answering it
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    (Original post by TeachChemistry)
    Electrophilic addition
    Nucleophilic substitution
    Free radical substitution
    Thanks, i find them so confusing
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    (Original post by _kirstxn)
    theres a question in the textbook on p.231 "How are harmful Nox and CO formed in a car engine?" i feel like i know the basics of the information but im a bit 'iffy' on how to go about answering it
    Try to answer it then check how you did vs. the p. 255 answer
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    (Original post by _kirstxn)
    theres a question in the textbook on p.231 "How are harmful Nox and CO formed in a car engine?" i feel like i know the basics of the information but im a bit 'iffy' on how to go about answering it
    Isn't it with the heterogeneous catalyst - adsorption, chemical reaction (bonds broken), desorption?
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    This is the mark scheme for 3)b), can someone explain why Concentrated H2SO4 is wrong? AQA AS

 
 
 
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