Notices
Results 1 to 9 of 9

Thread: Please don't hate me too much for asking this very basic question

  1. #1 Please don't hate me too much for asking this very basic question 
    New Member
    Join Date
    Sep 2014
    Posts
    3
    Hi,

    I work in a completely unrelated profession but am trying to get some science qualifications to improve my general understanding, and because from time to time it does assist with work.

    I'm doing a yr 12 chemistry equivalent by distance (no doubt extremely basic by the standards of some on here, but I have to start somewhere!) and am hoping for some help.

    I live in remote NSW so have no access to a face to face tutor.

    I'm having trouble with parts of questions involving balancing equations.

    (leaving aside the issues with super/subscript)

    1. Li+H2O - I understand that a metal + water = metal hydroxide + hydrogen gas, so I can get as far as Li + H2O = LiOH + H2 but I struggle when it comes to balancing the equation.

    2. Pb+O2 - I understand that a metal + oxygen = an oxide so Pb+ O2 = PbO, but again I'm stuck on the balancing issue.

    I don't really want answers to the questions - I need to have an understanding of the process so that I can answer future questions correctly and pass the final exam!

    Any help will be very gratefully received!


    Reply With Quote  
     

  2.  
     

  3. #2  
    Forum Junior
    Join Date
    Sep 2013
    Location
    Melbourne, Australia
    Posts
    281
    Balancing chemical equations is based on one of the fundamental principles, conservation of matter. In chemistry, the elements you start with will still exist in some form.

    So for your first case, with Li + H2O ----> LiOH + 2H, you have 1 more hydrogen as a product, so we modify H2O to 2H2O. Okay, now we have 4 hydrogen as a reactant, and 3 as a product, and we also have extra oxygen. So, if we were to add the coefficient 2 to LiOH, we would balance both the oxygen and the hydrogen. Now we have extra Lithium as a product, so then we finish it by changing the coefficient of Li to 2.

    Giving us 2Li + 2H2O -----> 2LiOH + H2

    So, based on this principle, have a go with the other one by yourself.

    And for the record, we never hate people who are interested in improving their understanding of science and keep an open, albeit sceptical mind, no matter how basic their questions.


    I can never know I'm right, but I can know that I'm wrong.
    Reply With Quote  
     

  4. #3  
    New Member
    Join Date
    Sep 2014
    Posts
    3
    Quote Originally Posted by Curiosity View Post
    Balancing chemical equations is based on one of the fundamental principles, conservation of matter. In chemistry, the elements you start with will still exist in some form.

    So for your first case, with Li + H2O ----> LiOH + 2H, you have 1 more hydrogen as a product, so we modify H2O to 2H2O. Okay, now we have 4 hydrogen as a reactant, and 3 as a product, and we also have extra oxygen. So, if we were to add the coefficient 2 to LiOH, we would balance both the oxygen and the hydrogen. Now we have extra Lithium as a product, so then we finish it by changing the coefficient of Li to 2.

    Giving us 2Li + 2H2O -----> 2LiOH + H2

    So, based on this principle, have a go with the other one by yourself.

    And for the record, we never hate people who are interested in improving their understanding of science and keep an open, albeit sceptical mind, no matter how basic their questions.
    Thanks for your reply and please excuse my ignorance here - I think the difficult I have is understanding why it is that we end up with one more hydrogen? Is the reason we end up with 4 hydrogen is because there are 2, and each is a diatomic molecule?

    I think one of my basic failings is being able to interpret the period table sufficiently to understand the charge of each ion so that I know what needs to be balanced?

    And the reason we are adding the coefficient of 2 to LiOH - is that because we ended up with the extra hydrogen?
    Reply With Quote  
     

  5. #4  
    Forum Junior
    Join Date
    Sep 2013
    Location
    Melbourne, Australia
    Posts
    281
    Don't need to worry about the charges of the ions in this case. Why in the sense of within the context of the formula? Because you have 2 moles of hydrogen as hydrogen gas, and one mole as part of lithium hydroxide, while you only have 2 moles of hydrogen as part of water, written as a reactant. It's simply a matter of counting the number of moles of the elements on both sides, and balancing them out by changing the coefficients.

    If you mean why why, it's because Hydrogen exists as a diatomic molecule when it's a gas, so H2 as opposed to H. But then, you've suddenly got one more mole of hydrogen that you didn't start with, which cannot be the case, so we simply go ahead and balance out the equation.
    I can never know I'm right, but I can know that I'm wrong.
    Reply With Quote  
     

  6. #5  
    New Member
    Join Date
    Sep 2014
    Posts
    3
    Quote Originally Posted by ohijustworkhere View Post
    Quote Originally Posted by Curiosity View Post
    Balancing chemical equations is based on one of the fundamental principles, conservation of matter. In chemistry, the elements you start with will still exist in some form.

    So for your first case, with Li + H2O ----> LiOH + 2H, you have 1 more hydrogen as a product, so we modify H2O to 2H2O. Okay, now we have 4 hydrogen as a reactant, and 3 as a product, and we also have extra oxygen. So, if we were to add the coefficient 2 to LiOH, we would balance both the oxygen and the hydrogen. Now we have extra Lithium as a product, so then we finish it by changing the coefficient of Li to 2.

    Giving us 2Li + 2H2O -----> 2LiOH + H2

    So, based on this principle, have a go with the other one by yourself.

    And for the record, we never hate people who are interested in improving their understanding of science and keep an open, albeit sceptical mind, no matter how basic their questions.
    Thanks for your reply and please excuse my ignorance here - I think the difficult I have is understanding why it is that we end up with one more hydrogen? Is the reason we end up with 4 hydrogen is because there are 2, and each is a diatomic molecule?

    I think one of my basic failings is being able to interpret the period table sufficiently to understand the charge of each ion so that I know what needs to be balanced?

    And the reason we are adding the coefficient of 2 to LiOH - is that because we ended up with the extra hydrogen?
    I'm very very grateful for your patience here Curiosity!

    So if I'm working forward...Pb+O2. A metal plus oxygen will form an oxide.

    Pb + O2 = PbO2...if there is nothing else created then there is nothing to balance?

    OR is it the case that because initially we have a diatomic molecule (oxygen) then we need two Pb to balance that out?

    2Pb +O2 = 2PbO2?
    Reply With Quote  
     

  7. #6  
    Forum Junior
    Join Date
    Sep 2013
    Location
    Melbourne, Australia
    Posts
    281
    No, you don't need extra Pb, because as you can see, the molecule PbO2 is just fine with one Pb and O2. Eventually you'll learn about what sort of compound is going to be formed by the oxidation numbers, but for now, you just need to worry about balancing out what you've been given.
    I can never know I'm right, but I can know that I'm wrong.
    Reply With Quote  
     

  8. #7  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,169
    Hi ohijustworkhere,

    take a closer look at your last equation:

    2Pb + O2 = 2PbO2

    On the left side of the equation you have two atoms of lead and one molecule, thus two atoms, of oxygen.

    But on the right hand side of the equation you still have two atoms of lead, but four atoms of oxygen. The equation is unbalanced. Your first version, however is balanced: one atom of lead and two of oxygen on each side of the equation.

    Keep in mind that just because we can balance an equation does not mean that the reaction will occur. It just tells us the proportion of reactants involved if it does proceed.

    If I may just emphasis a point made by Curiosity, regular members here sincerely welcome this sort of question. They get satisfaction from helping someone improve their understanding of a subject they personally find fascinating. Or, as in my case here, it gave me a chance to use a skill I haven't had occasion to use for a few decades.
    Reply With Quote  
     

  9. #8  
    Forum Junior
    Join Date
    Sep 2013
    Location
    Melbourne, Australia
    Posts
    281
    Well, I was given a lot of help by someone here when I was preparing for my exams for year 12 equivalent chemistry Feels right I should help others who are in the position I was in.
    I can never know I'm right, but I can know that I'm wrong.
    Reply With Quote  
     

  10. #9  
    Forum Ph.D.
    Join Date
    Jul 2011
    Posts
    985
    Refreshing to see a problem which I actualy can understand,
    Reply With Quote  
     

Similar Threads

  1. Question on QM basic measurements
    By Noa Drake in forum Physics
    Replies: 8
    Last Post: December 4th, 2013, 06:15 AM
  2. Basic Question
    By xingha in forum Astronomy & Cosmology
    Replies: 19
    Last Post: March 19th, 2013, 04:05 AM
  3. A Basic Geography Question
    By Nulledge in forum Earth Sciences
    Replies: 2
    Last Post: October 29th, 2010, 09:21 AM
  4. Basic battery question
    By niners in forum Electrical and Electronics
    Replies: 9
    Last Post: February 26th, 2009, 07:54 AM
  5. An absolute basic question
    By curious n sceptic in forum Physics
    Replies: 10
    Last Post: September 21st, 2007, 08:46 AM
Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •