scilearner

they are not dispersed in solution. the density doesn't change(except in extreme circumstances where you'd be using a different model anyway) therefore the concentration doesn't change.

 

for the water dissociation the water just has the same concentration. so the concentration of H3O and OH are the same. but if you take into account the volume you have more H3Oand OH than before.

Thank you for your help:-). But I didn't understand the last sentence. How can you have more H30 and OH if you have more volume?

Hello everyone,

Why is that liquids and solids have constant concentrations and are eliminated from equilibrium constants. I don't get it why can't their concentrations change. More importantly does this mean that if water (liquid) is a reactant in a reaction and if we add more water to the system the system would not move in the forward reaction to get rid of excess water. Help would be appreciated. Thanks

Example of my reaction 2H20 <> H30 + OH

Thank you Captain Panic and Hermantrude . I think I get it now. The 1 second example and the water bucket example were very helpful.. So with the water bucket example is this what happens

Intially one bucket was filled with water (reactants). First the water was poured it to another bucket very fast. Then as the water in the othe bucket increased the reverse reaction increases. Then it comes a stage where both people scoop only one cup of water at a second and this is equilibrium. Thanks again for both of you:-). I think I get it now.

Hello everyone,

It is funny that I thought I understood dynamic equilibrium really well but now I have gone blank again. I can do all the calculations and I understand

Le chatelier principle well. Here are the problems I have.

2A+B <----> C

* If forward reaction equals backward reaction wouldn't those two balance out and be zero. Is the reason why this doesn't happen is because both reactions are continuosly occuring. But please elaborate if you can.

*I checked so many sites on this topic and none of them really talks much about what happens to the moles in dynamic equilibrium. Can anyone tell me what happens to the moles in dynamic equilibrium. I understand that if the reaction occurs according to stoichiometric ratios there would be one way reaction. So roughly when we react 2 moles of A and 1 mole of B do we get like 0.8 moles of C.I'm just asking does something like this happen.

*If in equilibrium the reactants and products don't act according to their stoichiometric ratios why do we assume so in calculations. Do they always provide us with ICL data in equilibrium questions.

If anyone can take their time and at least answer one of these questions I would be very greatful. Thank you

Hello guys,

I know how to use the right hand palm rule. But I'm bit confused with the direction of the magnetic field.Let say current is into the page in a straight wire and then magnetic field is going on a circular loop and can be worked out accordingly with grip rule. But when I do the palm rule I don't know which way the magnetic field should be. There are so many places (I mean the which part of the circular loop that is perpendicular I choose.)Any help would be appreciated. Thanks!!

Hello guys,

This might be a simple concept for you guys but I'm bit confused. We are learning rates of reaction and why does a crushed tablet react quicker than a full tablet. Any diagrams to help me with this would also be great.

And while we are at I got few questions on equilibirum constant.

Let's say we have to write our own equation and let's say its a combustion reaction. We can choose if the product water is liquid or gas. But If choose liquid I won't be able to use it in the equillibirum constant Kp. So which state do I use

Why is temperature the only thing that changes th equilibirum constant?

Any help in any of these questions would be greatly appreciated.:-)Thank you!!

You obviously had a vertical component to get the answer. What was it?

No the question was just phrased like that. In the answer they have worked out the vertical component. You know like a projectile motion question. They have taken for vertical u=0 a=-10 t=1.5

v=u+at

= 15 m/s

They they worked out horizontal and used pythagorous therorm to work out the resultant vector. But in the question it says the rocket is always pointing horizontally so isn't the answer just the horizontal component?

V=u+at

= 0 + 34*1.5

= 66 m/s

Hello guys,

is there anyone who can help me with this motion question

I know how do it but I don't know why they do it like this

I'll write my question

An identical rocketrthat provides a constant force of 22 N (acceleartion=34 m/s/s) is now launched horizontally from the top of a 50 m tall bulding. Assume that in its subsequent motion the rocket always points horizontally. After 1.5 s what is the speed of the rocket. and at what angle is the rocket moving relative to the ground. I got the answers. The speed is 68 and the angle is 12 degress. You can get that from working out the vertical and horizontal components in the force. But how can there be a vertical component in this question.

Any help would be seriously appreciated!!

Thanks for the help YT2095:-). Well in the answer to this question it says that volatage of Rb =8.3. Only way to obtain thi is 9-0.7 is 8.3 which is the VRb but what happened to VRa. Don't we have to substract VRa as well to get the VRb.

Hello guys,

I'm struggling with these type of circuits. Here is my question. I have drawn a diagram in paint

When the input AC voltage= 0 v the collector current is found to be 1.0 mA. The current gain of the amplifier is 200. There must be 0.7 V between B and E before current can flow from the collector to the emmiter. What is the resistance of Rb

Well I know that Ai= Ic\Ib and I can find Ib but I don't know how to use this information. My understanding of series and parallel circuits is good but I don't know how this type of circuit works. If anyone can give me a detailed step by step of how this system works I'll be reallly really greatful

Thank you everyone who helped:-). Especially Janus. I think I get it now. The current took the path of least resistance in this circuit. Let's say there was a resistor in the wire with the switch then you would see more current flow to the globe. Am I right!!. Thanks a lot for the help guys. Really appreciate it.

What is the resistance of bulb C? What is the resistance of the wire with the switch in it?

Thank you for replying. This question is not about numbers and I think the resistance should be same because they are identical lamps. Why is that when te switch is closed that current only flows through A and B. I thought current would divide.

Hello guys,

I got a small question. It says circuit consists of three identical lamps connected to a battery with a switch as shown in the diagram. When the switch is closed what happens.

I did this really quick on paint.

It says that lamps C turns off because no current flows through it. But I don't get it. Shouldn't the current divide and each section get some current. Why is C getting no current when the switch is closed. Any help would be appreciated. Thanks

no... the current will stay the same. But, if you placed a larger resistor in there, how would that affect the voltage?

Then the volatage required would be high. V=IR. If resistance is the force that opposes the current why does it affect the volatge not the current. Thanks for the help by the way:-)

Why would the 300 ohms receive the least current? Where are the electrons going? You have a certain number of electrons moving through the wire and since they are in series, there aren't any branches for the current to take an alternate route. What comes in must come out.

Thanks for the help:-). I thought resistors decrease the current as the current goes through it. What does the resistor do. I'm talking about this formula where

I= V/R where R and I are inversely proportional.

Helllo guys,

I was wandering why was this the case. If there were 3 resistors (Let's say 100ohms,200ohms,300ohms) in this seriec how can they recieve the same current if resistance is inversly proportional to current. Shouldn't the 300 ohms one recieve the least current. I thought resistors decrease the current what do they really do. Any help would be appreciated. Thanks!! :-)

However, it is not true that current takes the path of least resistance — that's an oversimplification. If resistors 2 and 3 were unequal (say, R2<R3), the current (with the switch open) would not all flow through #2. The current flow would be proportional to 1/R, so that the voltage drop were equal across each.

 

Even in the example, if real wires are present, there will be a tiny current in 2 and 3 with the switch closed.

Thanks everyone who helped. Really appreciate it:-). I know how to work out the voltage when the switch is closed I just wanted to do know if it bipases in the second instance.I have another small question in a parallel circuit does some current flow to every circuit or does it take the path with least resistance.

Thanks everyone for your help now I understand what is going on. All this time I have being thinking about kinetic energy and confused my self. . So basically the only way voltage can drop is due to resistance isn't it. Thanks again!!

Hello guys:-),

I have one more question. I'm not really sure that the answer to this question is current pathway anyway

all the resitors are 100 ohms. Why is that when the witch is closed the voltage of resistor 1 is 15. Is it because when the switch is closed the current takes the path with least resistance. I checked about this least resistance thing in the internet and they say that it is not always the case. Any help would be appreciated. Thanks:-)

Thanks for everyone who replied:-). I only got a bit of time so I'll rephrase my question. The continued power source makes sense. My question in other words

is doesn't the electrical potential energy turn into electrical kinetic energy as the charges are moving. If so why is the voltage constant. Is it because of constant power source. What do resistors really do.

what makes you think the voltage doesn`t decrease?

even a length of copper wire has a resistance, all conductors do (except Super conductors of course).

 

the only difference is that Resistor will limit the current more effectively for it`s size than a huge roll of copper wire 2Kms long or something

Thank you for the help:-). Well my question is in question I see the volatge always the same. For example in a parallel circuit the resistor recieve the same voltage but when the charges move and you use potential energy how can they have the same voltage.

EDIT: I can understand how resistors change the voltage but shouldn't the volatge drop even without resistors. I mean if the charges are moving around and losing potential energy shouldn't the voltage change . I know you are right but I'm confused with this. Sorry for the strange question.

Hello guys ,

I got a small question with voltage and charge. If voltage provides potential energy for charges why doesn't the voltage decrease all the time when the charges are moving. I mean I only see voltage change when their are resistors and stuff but my question is shouldn't the voltage change all the time because the charges are losing potential energy as they are moving. Also can you explain potential difference to me. I'm bit confused with that. My electronic undertstanding is not really good and your help would be really appreciated:-):-):-)

Thanks a lot for taking your time to answer my question:-). Your explanation makes sense and now I have no problems with getting the answer to question 1. I'm still bit confused why the left the spectator ions. Can you help me further in that. Thank you once again:-)

Hello guys ,

I'm sitting for the chemistry exam this year and I have started studying for it. The spectator ions have being bothering me a lot recently. In the books I'm doing they neglect them sometimes and write ionic equations and do all sorts of stuff with it. I know specatator ions aren't involved in the reaction but I get confused with them sometimes.I'll post some multiple choice problems here to make it clear where my difficulties lie. The answers are also provided. So all I really want is to understand how to get the answer.

Problem 1

A standard solution of pottassium permenganate (KMn04) has a concentration of 0.0240 M. It is titrated against a solution of iron (II) sulfate. The equation fo the reaction is. Sorry I don't know how to put numbers underneath.

5Fe2+ + Mn04- + 8H+ = 5Fe3+ + Mn2+ + 4H20

15.60 ml of the KMn04 solution reacts exactly with 20 ml of the FeSO4 solution. The concentration of the FeSO4 solution, in M, is

The answer in the back of the book is 0.0936

My problem- K and S04 are not even in the equation of the question. I think it is because they are spectator ions. Then the only concentration I can find is the concentration of Fe2+. How is this the same as the concentration of FeS04

Problem 2

50 ml of 0.020 M solution of Ba(OH)2 is added to 50 ml of a 0.060 M solution of HNO3. The hydrogen ion concentration in the resulatant solution, in mole per litre, is

Answer in the back of the book: 0.01 M

My problem: Normally I work out the excess reactant in a question like this and see the moles in excess. But when I work out if Ba(0H)2 or HNO3 is in excess. I don't work out H+ ions. Can I get the moles of H+ ions in excess because it is equal to moles of HNO3 in excess. Does that mean if the reactant is H2NO3 ( I just made this up) instead of HNO3. I times by 2 to get the H+ ions in the resulatnat solution. Another problem I have is acid and base produce H20. Why don't we add the H+ ions in the H20 to the solution

Problem 3

20.0 ml of 0.10 M HCL reacts with 20 ml of 0.30 M KOH solution. The concentration of pottassium ions in the resultant solution, in mole per litre ,is

The answer in the back of the book- 0.15. They are saying that K+are spectator ions, hence n(K+) does not change. However the volume changes to 40 ml hence the concentration is halved.

My problem: Normally I find the excess and limiting reactant in a question like this. Then I look at the moles in excess and divide that by the total volume. Why is that moles of spectator ions do not change.

I don't expect you to understand everything I said. I tried my best to explain. If you can help me with these questions or pass any tips when working with spectator ion questions I'll very much appreaciate it . Thanks!!

What end result would you want to measure?

Fruits, growth. I'm not really sure. Just explain the answer please