Drake Glau Posted May 25, 2011 Report Share Posted May 25, 2011 (edited) Umm I'm not even sure what you're talking about O.o 2E+B->C+3D Kc=([C][D]3)/([E]2) Do you have an example possibly? I don't have a book anymore to look it up Couldn't use A for a reactant, kept thinking I was posting by Aboo...stupid bbc code... Edited May 25, 2011 by Drake Glau Reply Link to post Share on other sites More sharing options...
Hinuku Posted May 25, 2011 Report Share Posted May 25, 2011 (edited) Here you go : Kc = ([CH3COOC2H5(l)]eqm[H2O(l)]eqm)/([C2H5OH(l)]eqm[CH3COOH(l)]eqm) I just don't get what the "eqm" is for. And another question Using the following data. explain whether the above rxn is exothermic or endothermic: Temperature/K : 298; 500; 700 Kc/dm3mol-1: 9.77*1025;8.61*1011; 1.75*106 The values correspond to each other; e.g. 298 K was the rxn with Kc = 9.77*1025 I have no idea why I don't get this one, I think I did it a short while ago, I'm kind of tired I guess Thanks Edited May 25, 2011 by Hinuku Reply Link to post Share on other sites More sharing options...
Drake Glau Posted May 25, 2011 Report Share Posted May 25, 2011 It's denoting that the concentrations being used are the concentrations when the reaction has reached equilibrium.Endothermic.The Kc is dropping, which means you reactants is becoming more concentrated, meaning it's going in the left direction. So the left direction is heating up stuff, so left is exothermic, therefore the actual reaction (to the right) is endothermic. 1 Reply Link to post Share on other sites More sharing options...
dessskris Posted June 11, 2011 Report Share Posted June 11, 2011 (electrolysis) briefly explain why the volume of electrolyte in the half cells affects the current but does not significantly alter the voltage produced by the cell.I understand the voltage part, but the current??? help? Reply Link to post Share on other sites More sharing options...
Keel Posted June 11, 2011 Report Share Posted June 11, 2011 (electrolysis) briefly explain why the volume of electrolyte in the half cells affects the current but does not significantly alter the voltage produced by the cell.I understand the voltage part, but the current??? help?If there is a larger volume of electrolyte, there will be more ions. Thus the probability that an electron is transferred between the electrolyte and the electrode is higher which will then result in a higher current. Reply Link to post Share on other sites More sharing options...
dessskris Posted June 17, 2011 Report Share Posted June 17, 2011 I don't really understand....what actually determines the current in a voltaic cell? Reply Link to post Share on other sites More sharing options...
Sublime Sunshine Posted June 17, 2011 Report Share Posted June 17, 2011 Several factors affect the current of a voltaic cell. The major one is the strength of the oxidant and reductant. The further they are away from each other in the table in the data booklet, the greater the amount of current. The surface area of the electrodes would also affect the current. Not too sure about concentration of reactants, we did a prac on that but nothing much came out if it... it was a bit dodgy Reply Link to post Share on other sites More sharing options...
dessskris Posted June 17, 2011 Report Share Posted June 17, 2011 in an electrolytic cell, if the anode is zinc, the cathode is copper and the electrolyte is HCl, what reactions will occur? I am only in chem SL and even though I've learnt this before IB I can't remember. are they:2Cl- --> Cl2 + 2e (anode)2H+ + 2e --> H2 (cathode)?thanks. Reply Link to post Share on other sites More sharing options...
Drake Glau Posted June 17, 2011 Report Share Posted June 17, 2011 (edited) I don't really understand.... what actually determines the current in a voltaic cell? Concentration of the solutions will affect this. If the concentrations are higher then there is a greater amount of reactions occurring (increased rate) and these reactions are causing the movement the electrons. If more electrons are moving because there are more reactions occurring then your current will increase as more electrons travel through that wire in the same amount of time due to the increased rate of the reactions at the electrodes. And as Keel hinted at earlier, this is directly tied to collision theory, always good to include that if the actual exam asks about something like this. Chemistry likes its specific words in an electrolytic cell, if the anode is zinc, the cathode is copper and the electrolyte is HCl, what reactions will occur? I am only in chem SL and even though I've learnt this before IB I can't remember. are they: 2Cl- --> Cl2 + 2e (anode) 2H+ + 2e --> H2 (cathode) ? thanks. Anode might make ZnCl I think (I didn't bother crossing charges, don't think you need to but didn't feel like looking it up right now ) but if not you're right Edited June 17, 2011 by Drake Glau 1 Reply Link to post Share on other sites More sharing options...
dessskris Posted June 17, 2011 Report Share Posted June 17, 2011 then does the concentration only affect the rate of reduction reaction, or also the rate of oxidation reaction? because the oxidation does not require the ions in the electrolyte (only the metal electrode). while the reduction requires the ions in the electrolyte.for the other question, how do I know which reaction occurs at the anode (oxidation of chloride ion or of zinc electrode)? Reply Link to post Share on other sites More sharing options...
Drake Glau Posted June 17, 2011 Report Share Posted June 17, 2011 then does the concentration only affect the rate of reduction reaction, or also the rate of oxidation reaction? because the oxidation does not require the ions in the electrolyte (only the metal electrode). while the reduction requires the ions in the electrolyte. for the other question, how do I know which reaction occurs at the anode (oxidation of chloride ion or of zinc electrode)? We were talking about concentrations in voltaic cells O.o Both parts of the cell have their own reactions that are affected by the concentration. Remember to keep your two types of cells separated Oxidation removes electrons, think about ionization energies. If you have a cation already, "missing" electrons, and an anion, with "extra" electrons, which one is easier to take electrons from? The cation has a much higher ionization energy since the charge from the nucleus is spread over a fewer number of electrons (this is assuming they're in the same period...I think they are O.o) so it'd be easier to just take electrons from the anion (Cl). I guess you would end up with chlorine gas...well you could end up with a lot of things but I could just be over thinking this. 1 Reply Link to post Share on other sites More sharing options...
dessskris Posted June 17, 2011 Report Share Posted June 17, 2011 uh yes I'm talking about voltaic cells too... say I use zinc and copper electrodes, with CuSO4 electrolyte. which reaction does the volume of electrolyte affect? is it only the reduction of copper ions at the cathode? or also the oxidation of zinc at the anode? if also the oxidation, why? I thought it's got nothing to do with the ions i.e. electrolyte? alright that makes sense... actually we did an experiment on this but there were 2 electrolysis experiments and this one was done by the other group (my group did the other experiment that was simpler ) so I didn't really remember the results... I only remember hydrogen gas at the cathode but yeah I think there was also chlorine gas. thanks for confirming! Reply Link to post Share on other sites More sharing options...
Drake Glau Posted June 17, 2011 Report Share Posted June 17, 2011 uh yes I'm talking about voltaic cells too... say I use zinc and copper electrodes, with CuSO4 electrolyte. which reaction does the volume of electrolyte affect? is it only the reduction of copper ions at the cathode? or also the oxidation of zinc at the anode? if also the oxidation, why? I thought it's got nothing to do with the ions i.e. electrolyte? alright that makes sense... actually we did an experiment on this but there were 2 electrolysis experiments and this one was done by the other group (my group did the other experiment that was simpler ) so I didn't really remember the results... I only remember hydrogen gas at the cathode but yeah I think there was also chlorine gas. thanks for confirming! 1. Volume would affect both. If one side runs out the whole cell stops because the ions stop moving and then charges go back to normal and nothing happens. Volume really doesn't affect reactions all that much except for how long they will last simply because there are more particles to react with. 2. Yes. It has nothing to do with the electrolytes, directly (the electrolyte runs the whole show with the salt bridge keeping things the charge they need to be for the cell to work). The copper is reduced, meaning it used 2 (probably) electrons, well they needed to come from somewhere and they came from the zinc anode where it was oxidized which is where the electrons came from. 1 Reply Link to post Share on other sites More sharing options...
ILM Posted June 17, 2011 Report Share Posted June 17, 2011 (edited) hey, I have a question about lewis structure, how to know that there is a dative bond, and when to know that the atom will share more electrons than usual for example ClO4 Edited June 17, 2011 by inm Reply Link to post Share on other sites More sharing options...
nametaken Posted June 17, 2011 Report Share Posted June 17, 2011 (edited) In some cases you can't really tell just by looking at the molecule - which atom provided the electron pair to form the dative covalent bond as the electrons are identical. But I think that you could sort of tell if one of the atoms is forming more bonds than usual (than bonding to the required number of electrons to complete its outer shell). Like say for H3O+ or NH4+ oxygen is forming three bonds instead of two, nitrogen is forming four instead of three so you could sort of tell that one of them isn't a normal covalent bond as oxygen would otherwise be unable to form three, nitrogen four since they would already have a full outer shell. They do not need any more electrons or to form any more bonds to attain a stable electronic structure. Therefore one of the covalent bonds must be dative with the bonding electron pair being provided by the oxygen / nitrogen without sharing any more electrons from the hydrogen into its outer shell since O/N no longer has any unpaired electrons to share (no singly occupied orbital to interact). Edited June 18, 2011 by nametaken 1 Reply Link to post Share on other sites More sharing options...
Keel Posted June 18, 2011 Report Share Posted June 18, 2011 hey, I have a question about lewis structure, how to know that there is a dative bond, and when to know that the atom will share more electrons than usual for example ClO4Hi,Lewis structures can be extremely hard to get the hang of but only because you don't have a clear cut procedure to follow. Here are the steps I follow:Identify the central atoms and draw the electrons in its outer shell Draw the other atoms around (but not joined to) the central atom; draw in their outer shell If the entity is a negative ion add an electron for each negative charge. Add to the most electronegative atom. If the entity is a positive ion remove an electron for each +ve charge. Remove from the least electronegative atom. Decide how the electrons can be paired up Check that all atoms have the allowed number of outer shell electrons; 4e: BE; 6e: B, Al; 8e: C, O, N, F; 8-12e: P,S and Cl/anything with d orbitals: 8~14e If point 5 is not met then one bond must be dative.The expanded octet will only apply to the central atom which is identified in the first step.Less than 8e: Be, B, AlFollows octet rule: C, O, N, FCan obey octet rule or have greater than 8e: P, S, Cl, Br, I (basically anything from Cl onwards) 1 Reply Link to post Share on other sites More sharing options...
Hinuku Posted June 23, 2011 Report Share Posted June 23, 2011 (edited) Hi, I have this problem with calculating the overall Ka value. Does anyone know how to do this? It is a triprotic acid and so it has 3 dissociation constants but I read that it is possible to obtain a general one, I just can't find how. Thanks, Matt Edited June 23, 2011 by Hinuku Reply Link to post Share on other sites More sharing options...
Drake Glau Posted June 24, 2011 Report Share Posted June 24, 2011 Do you have any other information? There's an equation for this if you have more information for us Reply Link to post Share on other sites More sharing options...
Rigel Posted June 24, 2011 Report Share Posted June 24, 2011 Isn't that related to Equilibrium? Reply Link to post Share on other sites More sharing options...
Drake Glau Posted June 24, 2011 Report Share Posted June 24, 2011 It is sort of, yes. This is why it helps to have more information, volumes? mass? concentrations? etc...those can all lead to the stuff you need for this Reply Link to post Share on other sites More sharing options...
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