Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    1
    ReputationRep:
    Suggest why the addition of anhydrous magnesium chloride to water resultsin an increase in temperature?

    The markscheme says that the answer is" the bonds created between the Mg2+ and cl- ion release energy as bond making is exothermic"

    I dont understand as I thought when ionic compounds dissolve they are pulled apart due to the electrostatic attractions between the polar water molecules and the ions. Why are they bonding together again?

    Thanks
    • Thread Starter
    Offline

    1
    ReputationRep:
    any ideas?
    Offline

    2
    ReputationRep:
    When Magnesium Chloride dissolves in water, the Mg2+ and Cl- ions dissociate in solution, of course energy is required to break the lattice structure. However, an excess of energy is in fact released from the ionic bond making of water molecules surrounding the Mg2+ and Cl- ions, so-called 'clustering' of water molecules. Overall, more energy is released from the process of dissolving/bond making, this means the reaction is exothermic. Hence an increase in temperature.

    This image shows a similar situation when Sodium chloride dissolves, notice the partial negative and partial positive charges of a water molecule.

    Name:  dissolving.jpg
Views: 39
Size:  7.9 KB
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by RDB1826)
    When Magnesium Chloride dissolves in water, the Mg2+ and Cl- ions dissociate in solution, of course energy is required to break the lattice structure. However, an excess of energy is in fact released from the ionic bond making of water molecules surrounding the Mg2+ and Cl- ions, so-called 'clustering' of water molecules. Overall, more energy is released from the process of dissolving/bond making, this means the reaction is exothermic. Hence an increase in temperature.

    This image shows a similar situation when Sodium chloride dissolves, notice the partial negative and partial positive charges of a water molecule.

    Name:  dissolving.jpg
Views: 39
Size:  7.9 KB
    Thank you!
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Brexit voters: Do you stand by your vote?
    Help with your A-levels

    All the essentials

    The adventure begins mug

    Student life: what to expect

    What it's really like going to uni

    Rosette

    Essay expert

    Learn to write like a pro with our ultimate essay guide.

    Uni match

    Uni match

    Our tool will help you find the perfect course for you

    Study planner

    Create a study plan

    Get your head around what you need to do and when with the study planner tool.

    Study planner

    Resources by subject

    Everything from mind maps to class notes.

    Hands typing

    Degrees without fees

    Discover more about degree-level apprenticeships.

    A student doing homework

    Study tips from A* students

    Students who got top grades in their A-levels share their secrets

    Study help links and info

    Can you help? Study help unanswered threadsRules and posting guidelines

    Sponsored content:

    HEAR

    HEAR

    Find out how a Higher Education Achievement Report can help you prove your achievements.

    Groups associated with this forum:

    View associated groups
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Write a reply...
    Reply
    Hide
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.