scilearner

Thanks once again I can understand how this would create higher pressure lower down but how is this related to density. Warm air is more dense than cold air so how is cold air at the top be less dense. Merged post follows: Consecutive posts mergedI'll make my question in form of a picture

Thanks for the reply Sorry my science knowledge is not very good and I couldn't really understand. So if it compacts wouldn't it be more dense higher up.

Hello everyone I'm just wondering why is cooling considered to slow reactions. I mean f you want condensation heating would slow the reaction. I like to know exactly how condensation occur at molecular level. I know when you heat gas it expands. So when you cool a gas does it contract, and where does the energy for change phase from gas to liquid come from. Does cooling provide energy too like heat. Why is that when cooling in this case there is not much kinetic energy but a reaction (condensation) takes place. Your help would much appreciated thanks!!

Hello everyone I have a quick question why is the air less dense higher up you go. I can understand air expands and the volume is bigger hence less dence but that only happens if it is warm, higher you go it is cooler so how does air expand. Thank you!!

Hello everyone , I have some questions about standing waves and guitar. In a guitar why is the fundamental frequency the centre of the guitar. Why isn't it just when you play an open string. How do different strings in guitar produce different sounds. Don't they have the same length hence the same frequency. Even though standing waves are produced in the strings when we listen it travels in air. Does this mean the wavelength of the standing waves is different in air or is it the frequency that is different. Thanks a lot!!

Thanks both of you for your replies Oh I didn't realized the that it is not against time. However in my notes there is exactly the same graph but the displacement graph has time in the x axis . This is the closest pic I found in the internet. So treat the x axis as time and explain. Thank you

Hello everyone , I'm so confused with particle displacement vs time graph and pressure vs time graph of sound. I thought maximum displacement of a particle is its compression and minimum displacement is its rarefaction. For some strange reason the graphs show exactly the opposite. How can the particles be at atmospheric pressure when the displacement is maximum. Your help would be greatly appreciated. Thanks

Thanks both of you for your replies. That was a good respone, big314mp I like to understand the way you have showed. However I can only do it if I know how this meaningless equilibrium is caused? Can anyone explain me to how is these two equilibrium caused in these two cells?

No probs. I didn' know there was a system like this here. I didn't think I expressed myself clearly last time. If you can please answer this question I'll sure add more scales . This is my confusion chemguide says..... In respect to your previous post "half-reactions cannot occur on their own" In this case is this equlibrium caused by this equilibrium I mean one cannot occur without the other Would these equilbrium rise if the cells were not connected. However I get the feeling chemguide is suggesting that these equilibrium would exist if these cells were not connected. I'm not sure. If my understanding is wrong please tell me how this equilibrium have occured. Yes you probably have mentioned this in previous post but could you please reexplain this with this specific example. I'll be most greatful. Thanks

Thanks a lot Hermantrude . I have tried to get help for this question from variety of sources but I think you have understood my question better than anyone else. I especially liked the water equation that makes a lot of sense why Mg dissolves. Yeah we just finished equilibrium and totally forgot about that fact that everything is in equilibrium. I'm pretty sure you meant products. Yeah!! Ok now I'm going to make a topic on the daniel cell. I want to see if my understanding on that is right and I got some problems with inert electrodes. Looking forward to your help there especially!! Also thanks for understanding I'm a begginer and would not be able to grasp some of the concepts immediately. Thanks again!! PS: Just one more question. If Mg electrode is left in a solution of Mg2+ not water there would be an equilibrium right between the ions and the solid Mg <----------> Mg 2+ + 2e- Here the two half reactions are the forward one and backone. I'm assuming here the Mg2+ can act as the oxidant!!

Thanks a lot!!. This is actually one of the most satisfying answers I have recieved Only few problems. So how is equilibrium related to all this. Is the Mg 2+ formed in equlibrium? Does redox equlibrium occur only when elements are in a solution such as this!! Can same be said of Mg ions in a solution. Would they try to use water's half equations and create this same equilibrium. Mg <------> Mg2+ + 2e- Thanks again

Hello everyone I thought before I could move to the daniel cell I have to understand this concept. 1. If we leave Mg solid electrode in water it says there is a tendency for Mg to dissolve into ions creating equilibrium Mg <-------> Mg2+ + 2e- I thought one half reaction cannot occur independant of the other half reaction. I mean oxidation and reduction should always occur at the same time. I understand here that forward is oxidation and backward is reduction. So is this true that this happens when you put Mg in water. 2. How about Mg+ ions in an solution would they create an equilibrium like this or is it only solids that can dissolve create this equilibrium? 3. So after looking at redox equilibrium this is my new understanding of redox equations. Tell me if this is right . 1. There is zinc in a glass tube It is in equilibrium Zn <-----> Zn2+ + 2e- 2. There is Mg in another glass tube It is in equilibrium Mg <-----> Mg2+ + 2e- 3. You add them together and then according to their potentials one reaction gives electrons to another reaction. The equilibriums of each reactions is upset and they eventually become oneway reactions. So infact the halfway reactions are occuring all the time it is just that redox reactions upset the equilibrium and make them oneway reactions. Am I right? Thank you

Thank you everyone for your help. So in sound amplitude is not measured in m is it measured in terms of pressure. Particles in a sound wave are travelling back and forth parallel to the direction of the wave. How are they moving up and down. Isn't that transverse wave? Ok I edited the image of the sound wave and divided it in to sound waves. So I'm assuming the amplitude here is the thickness of the lines and wavelength is the distance between the lines. Am I right? Looking forward to your replies Thanks again for each and everyone who has replied

Hello everyone, I understand wavelength,frequency but not the amplitude. Can anyone here explain what do they mean by the amplitude. In some places they say it is the maximum displacement of a particle but isn't this the wavelength. My other confusion with sound is this Ok here the amplitude is the top bit from the graph. So it is maximum change in pressure. So why is it measured in m. Can anyone tell me what does this mean in particle level. If this is how sound spreads in all directions. I don't get it. Shouldn't sound follow a straight path like the longitudinal wave in the top picture. I thought sound was a longitudinal wave then why is travelling circular like this. Can anyone relate the longitudinal wave with this pic and tell how are they related. Is the wavelength in this case the distance between two waves or Inside each ripple is their a longitudinal wave? Any help in any of these questions would be much appreciated :-) :-)

Thanks everyone who has helped :-):-) . I think I'm getting it now. I still got few more questions. So when the water pulls apart the molecule to ions and the water surround these ions, how can they react again? This equation is from the top of my head so might not be right. I hope you get the idea though Example of what I'm talking about NaCl (aq) + KI (aq) react. The products would be NaI and KCl. Why does Na react with I why can not it just recombine with Cl and not take part in a reaction. I mean if all the ions in this reaction are surrounded by water molecules how can they react? Why does Na+ choose I- rather than Cl- Why can not an ion exist by itself? Is this because the atom does not have another atom to lose or gain nessecary electrons to be an ion. Is this role of the spectator ions. Helping the atoms required to be ions. Am I right? @ frosch45 The video was great . Good references Thanks

Thanks a lot for your help frosch45 . I had a think about what you have said and it makes sense. Now however I have few more questions Is an ion stable or not? Ion's have stable valence outershell hence I think they are stable. So why do they react to form NaCl. Is it simply because unlike charges attract and not actually to be stable. I mean if Na+ exist by itself is it fair to say it is stable. My other questions is how can a solution of NaCl dissocitae to Na+ and Cl-. Wouldn't they attract like magnets forming NaCl again.

Hello everyone, I'm confused with the definition of an ion. Does an ion mean an atom that has lost or gained an electron or an atom that has the potential do so. For example Na+ + Cl- --------- NaCl In this case doesn't Na+ mean it has a potential to lose an electron. I mean NaCl would be formed if this happens. But if we write Na+ at the start doesn't it give the impression that Na+ has already lost an electron. 2nd example NH3 + H+ ---------- NH4 In this doesn't H+ mean it has already lost an electron (not has the potential to). Then acid base reaction occurs to form NH3 Can you understand my point isn't it bit inconsistent the definition of an ion because sometime it means it has the potential to lose electrons. Any help on this would be greatly apprecitated.

Thanks a lot for the reply ecoli . It was just what I was after . So the commutator is just like a common sense arrangement to reverse the current. The way our school teaches is that it is some kind of device where some chemical reaction occurs inside to reverse the current . So the commutator doesn't actually reverse the current by some reaction inside. So it is just a common sense arrangement and the rotation of the coil ensures the current is reversed. Am I right?

Hello everyone, I have a simple questiom about the DC motor. I understand that in the DC motor the commutator reverses the current to get a constant rotation but my question is why do we really need one. For example in this diagram If the only thing that rotates is the coil and the commutator wouldn't the current always be in the same direction. I mean the only way the current could change is if the whole circuit turns as well with the coil and commutator. Put it simply I don't understand why the current reverses every half a rotation when only the coil and the commuatator is rotating. I made another different topic about commutator in physicsforums and didn't get a single reply. I hope scienceforums would do better . Your help would be greatly appreciated

Thanks everyone who helped . Yes understand now this is a case where the electrons are inside the wire so we have to use conventional current. Yeah I agree with the conventional current. I don't like it too much. Thanks again everyone who helped

Hello everyone, I got a question Electrons moving through a resistor experience a force if the resistor is in a magnetic field. A resistor is oriented east west as shown with the earth's magnetic field into the page -----------XXXXXX-----------> (Direction of current given) X- Magnetic field into the page An electron travelling through the resistor will experience a force due to the magnetic field which is A Up B Down C into the page D out of the page Ok the answer that is stated is A. Yeah I know you can get this by using the simple right hand palm rule. My problem is I thought electron move in the opposite direction to the conventional current. So don't we have to take current as left and the answer is B. Also bit off topic why is that in an electron charge we take the direction of current as the opposite to the given current. Is it for the same reason I just said above. So isn't this a question like electron charge. Any help would be appreciated. Thanks

Yeah I made up the water example and I asked one of my teachers and she said acidity decreases . lol it's not her fault I think I did a bad job at explaining my question . Anyway I have one more question If 0.10 M Mg(OH)2 calculate the PH I know how to do this. Why can we use mole ratios to work out concentrations. I thought it was only for moles. So when mgoh2 is dissolved do I have to think of concentration of OH going up or concentration of H30 going down at equilibrium. When working out the concentration of OH do we have to assume that the concentration we work out is the concentration of OH when the equilibrium position has moved to the left. Thanks a lot for your help so far You are the only one who has helped so far

Thanks a lot for your help Insane Alien . I had a good think about the moles and worked it out. When we add water there is more water and concentration is decreased. If moles in increases you can get closer to the intital level. What you are saying should be true because if the concentrations do not change to their initial level. The PH of water would change. This can only happen at temperature. I think why I'm confused is that I have never seen what Le chatelier principle state when both product concentrations are decreased at the same time. Le chatelier only talks about one reactant or product or when the whole concentration of products and reactant are decreased. So according to Le chatelier principle if the concentration of H30, OH would go down at the same time if water is added. Concentration of water wouldn't change because of liquid. Then how can the concentration come to back to intitial level if the system only partially counteracts the change. But what you are saying must be right because or else Kw would change. Looking forward to your reply

Thanks once again for the help and understanding . Or is it that even though the moles are increased the volume is also increased at the same time. So the probababily of fruitful collisons are still the same. I think I got it . So in equilibrium if you add solid or liquid does that mean there would be no effect. Still I'm bit confused with having more moles of H30 and OH. If the concentration of water stays the same with added water wouldn't the concentrations of H30 and 0H... Oh I get it so if this didn't happen in water and if we added more solid the concentrations of the products and the moles would stay the same. Basically no effect. Am I right? EDIT: Actually now I think about it. When an acid and a base react water is produced. If there is no limiting or excess in this case. So wouldn't this water produced create a dilution. Making H30 and OH gone down. According to Le chatelir the reaction would try to move to more particle side. But both sides have same number. So isn't the concentration going down.

Thanks once again for your help . Are you saying concentrations stay the same because of particles in both sides being equal or water that has a constant concentration is added. This is where I'm most confused. If you add more water do you increase the moles of water. If so wouldn't there be a faster reaction with more moles of reactants?