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    Hi,
    I’ve been stuck on this question for a bit now.

    A mass of 0.35kg ice at -15∘C is lowered into an insulated beaker containing water at 59∘C
    . What is the minimum mass of water at this temperature needed in the beaker to achieve a final temperature of 0.0∘C?

    From previous parts of the question I worked out that it required 10657.5J to heat the ice to 0 degrees, it then required an additional 117250J to melt the ice.

    I think I need to use Q=mc delta T with the smallest value of Q that I can but I’m not sure what value of Q I need as I tried 10657.5 and got a mass of 0.043kg but it said that although that results in 0degrees it isn’t the smallest mass.

    Any help would be much appreciated
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    (Original post by Snoozinghamster)
    Hi,
    I’ve been stuck on this question for a bit now.

    A mass of 0.35kg ice at -15∘C is lowered into an insulated beaker containing water at 59∘C
    . What is the minimum mass of water at this temperature needed in the beaker to achieve a final temperature of 0.0∘C?

    From previous parts of the question I worked out that it required 10657.5J to heat the ice to 0 degrees, it then required an additional 117250J to melt the ice.

    I think I need to use Q=mc delta T with the smallest value of Q that I can but I’m not sure what value of Q I need as I tried 10657.5 and got a mass of 0.043kg but it said that although that results in 0degrees it isn’t the smallest mass.

    Any help would be much appreciated
    There is no description of the final state of matter in the beaker... I guess you don't need to consider the energy used to melt the ice - a beaker containing ice at 0.0 degrees is sufficient to answer the question.
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    (Original post by Joinedup)
    There is no description of the final state of matter in the beaker... I guess you don't need to consider the energy used to melt the ice - a beaker containing ice at 0.0 degrees is sufficient to answer the question.
    That’s what I thought, the values I used came from just the energy needed to heat the ice to 0 degrees so I have 0 degree ice in 0 degrees water.
    The hint at the end has said think about the energy transferred as ice goes to water and vice Versa. But I can’t think of any way of using that info.

    Thanks again
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    (Original post by Snoozinghamster)
    Hi,
    I’ve been stuck on this question for a bit now.

    A mass of 0.35kg ice at -15∘C is lowered into an insulated beaker containing water at 59∘C
    . What is the minimum mass of water at this temperature needed in the beaker to achieve a final temperature of 0.0∘C?

    From previous parts of the question I worked out that it required 10657.5J to heat the ice to 0 degrees, it then required an additional 117250J to melt the ice.

    I think I need to use Q=mc delta T with the smallest value of Q that I can but I’m not sure what value of Q I need as I tried 10657.5 and got a mass of 0.043kg but it said that although that results in 0degrees it isn’t the smallest mass.

    Any help would be much appreciated
    Figured it out?
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    (Original post by I'msoPi)
    Figured it out?
    Yeh, in the end my teacher proudly told me she had managed all but one question, that question🤦*♀️ but then we had the sudden realisation that the hot water turned into ice as that released more energy. From there it was ok.

    Edit: and yes, it took 7 months for us to solve it!
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    (Original post by Snoozinghamster)
    Yeh, in the end my teacher proudly told me she had managed all but one question, that question🤦*♀️ but then we had the sudden realisation that the hot water turned into ice as that released more energy. From there it was ok.

    Edit: and yes, it took 7 months for us to solve it!
    Ahaha can't believe you responded even though this was from months ago. I'm doing that question now so lemme give it another crack knowing that it turns to ice
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    (Original post by I'msoPi)
    Ahaha can't believe you responded even though this was from months ago. I'm doing that question now so lemme give it another crack knowing that it turns to ice
    Notifications appear when I’m waiting for a stream to start, made me laugh remembering the annoyance that was this question!
    Oh and good luck with it.
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    (Original post by Snoozinghamster)
    Notifications appear when I’m waiting for a stream to start, made me laugh remembering the annoyance that was this question!
    Oh and good luck with it.
    Stream? ergh my brain is actually too frazzled at this point to complete this question lol
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    (Original post by I'msoPi)
    Stream? ergh my brain is actually too frazzled at this point to complete this question lol
    Stream-Show on twitch someone gaming

    If you try again and It doesn’t work let me know and I’ll try and explain it better
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    (Original post by Snoozinghamster)
    Stream-Show on twitch someone gaming

    If you try again and It doesn’t work let me know and I’ll try and explain it better
    Ah yeah I thought it was something on twitch. Thermal physics is killing me softly, would you mind explaining it :sigh:
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    (Original post by I'msoPi)
    Ah yeah I thought it was something on twitch. Thermal physics is killing me softly, would you mind explaining it :sigh:
    I can certainly try.

    When ice melts into water that takes energy, when the same mass of water freezes that releases the same amount of energy.

    So here we have ice at a cold temperature so we need to raise it up to 0 degrees, we can work out how much energy is needed by Q=mc \delta T. This is the energy we need.

    The water is at 59 degrees so we need to work out how much energy is released in cooling it to zero. (This will be in terms of m)

    Then the bit that I didn’t know to do.
    You need to work out the energy released in freezing the water using the latent heat of fusion times mass.

    The energy needed to warm the ice = the total energy released.

    From here you just rearrange to find m.

    Hoops that helps
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    (Original post by Snoozinghamster)
    I can certainly try.

    When ice melts into water that takes energy, when the same mass of water freezes that releases the same amount of energy.

    So here we have ice at a cold temperature so we need to raise it up to 0 degrees, we can work out how much energy is needed by Q=mc \delta T. This is the energy we need.

    The water is at 59 degrees so we need to work out how much energy is released in cooling it to zero. (This will be in terms of m)

    Then the bit that I didn’t know to do.
    You need to work out the energy released in freezing the water using the latent heat of fusion times mass.

    The energy needed to warm the ice = the total energy released.

    From here you just rearrange to find m.

    Hoops that helps
    Yay I just got it now thanks!! Although I don't fully understand why I didn't have to use the energy required to melt the ice (the latent heat one) but i'm assuming it's just because it doesn't actually melt?
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    (Original post by I'msoPi)
    Yay I just got it now thanks!! Although I don't fully understand why I didn't have to use the energy required to melt the ice (the latent heat one) but i'm assuming it's just because it doesn't actually melt?
    Yeh the ice doesn’t melt as we want the minimum energy required to get it to 0 degrees and it would require additional energy to melt the ice
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    (Original post by Snoozinghamster)
    Yeh the ice doesn’t melt as we want the minimum energy required to get it to 0 degrees and it would require additional energy to melt the ice
    Ahhhh okay thanks again for the help. I'm in a good mood now that this is finished lol
 
 
 
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