Biology; Chemistry; Physics: Post your doubts here!

[SalmanPakRocks]

lets calculate the number of moles in both
there are 2 moles in N2+H2
so it will need 48 dm^3
while in NH3
it only has one mole so it will need 24dm^3

So the forward reaction requires less space, increasing the pressure will help in more ammonia being formed cuz forward reaction need less space while backward needs more.

 

[scouserlfc]

e) suggest a suitable method for investigating the effect of a given variable on the speed of a reaction.... i dont understand what does this part means

This here mate requires u too remember some experiments which will help u in finding the effect of a given variable like temperature,surface area of particle on the speed of a reaction !

Like for comparing the speed of increasing temperature u can use a set up which has gas collection the amt of gas collected per minute can be used to find the increase in rate of reaction by increasing the variable that is temperature !

I dont think u got it i was in a hurry and i wrote something which is not understandable in that case ill tell u later perhaps on the weekend !

 

[snowbrood]

can anyone tell me why freezing and condensation is exothermic reaction... as my book says the temperature of the reaction rises in exothermic reactions... need immediate help guys

 

[SalmanPakRocks]

can u tell me why freezing and condensation is exothermic reaction... as my book says the temperature of the reaction rises in exothermic reactions... need immediate help guys

See learn this by heart
When a reaction gives off heat its exothermic reaction. Enthalpy is always in negative.
When a reaction takes heat from the surrounding its endothermic and entalpy is positive.

 

[snowbrood]

See learn this by heart
When a reaction gives off heat its exothermic reaction. Enthalpy is always in negative.
When a reaction takes heat from the surrounding its endothermic and entalpy is positive.

but again can u help me with this it is very confusing man i have done much of chemistry but this part seems pretty challenging for me as it is harder for me to memorize anything without its concept

 

[SalmanPakRocks]

hmmmm then learn this
exo = out
endo = enter.

 

[snowbrood]

See learn this by heart
When a reaction gives off heat its exothermic reaction. Enthalpy is always in negative.
When a reaction takes heat from the surrounding its endothermic and entalpy is positive.

i dont get the rise in temperature part how come a reaction get hot while its freezing man it goes over my head

 

[SalmanPakRocks]

hmmmm freezing as exothermic ? it is confusing, but i will conform it and let u know.

 

[snowbrood]

hmmmm freezing as exothermic ? it is confusing, but i will conform it and let u know.

you dont have to conform anything believe me its in my book and also in your notes(35106152-O-level chemistry)

 

[SalmanPakRocks]

ok then maybe someone else can explain us the concept here.
let's wait.

 

[snowbrood]

can anyone explain me the reactions at anode and cathode of fuel cell??

 

[CaptainDanger]

you dont have to conform anything believe me its in my book and also in your notes(35106152-O-level chemistry)

When something freezes bonds are made... When bonds are made energy is given out... Making it exothermic.... Or take it the other way, when it freezes, heat is given out and it cools down... Heat given = exothermic... Same goes for condensation...

can anyone explain me the reactions at anode and cathode of fuel cell??

Can you elaborate it a bit?

 

[legion]

how do we calculate the center of gravity of a plane lamina in theory paper? i mean we can do it in practical but what about in theory????

 

[SalmanPakRocks]

I think it is calculated the same way, using bob and hanging on each corner wala method.

 

[Sweetsilly]

Can someone answer me this question. i always get confused in it.
Q- Why the amoeba living in fresh water have contractile vacuole, whereas the amoeba living in sea water do not have any contractile vacuole?

 

[daredevil]

Re: Biology,Chemistry & Physics Help Available Here !



Your question is wrong. Barometer measures liquid pressure. Manometer measures gas pressure. You should learn it. It's confusing , and would cost you later on , so get it straight. Manometer measures gas pressure and barometer measures liquid pressure.

Barometer :
Refer to the book for the diagram. Uses the relation :
Pressure in liquid = Density of liquid x gravitational field strength x height of liquid coloumn.

So in other words if any one of the the three varies , the liquid pressure would vary accordingly. For example if a denser liquid is used , the pressure will increase. If the length is increased the pressure increases. But the gravitational field strength will not change as it is the same everywhere on the planet , but if it were to change , yes the pressure would increase.


Manometer :
Refer to book for diagram. ( it is advised you keep the diagram with you while reading this)
Now as you can see a manometer is a U shaped tube. If you pour liquid into it , the liquid levels reach the same height of both sides. Now to measure the gas pressure , you attach a gas supply to one end. If the gas pressure is more then atmospheric pressure ,then the liquid level will fall in the attached tube. Accordingly the level will rise in the other tube. The level that falls and the level that rises are equal. i.e if the level that has fallen is 2 cm , then the level that rose is also 2 cm. The gas pressure is calculated by adding both levels.

Pressure of gas = Level of liquid that falls + Level of liquid that rises.


Hope this helped.

so it means (the thing u said abt the formula in manometer) the pressure of the gas in the xample u gave will b 4 cm?

 

[fatikhalid]

The diameter and the length of a thin wire, approximately 1 m in length, are measured as accurately
as possible.
What are the best instruments to use?
diameter length
A micrometer rule
B micrometer vernier calipers
C rule tape
D vernier calipers rule

 

[Silent Hunter]

ok then maybe someone else can explain us the concept here.
let's wait.

maybe cuz exo means heat given out......... when heat given out... the inside temperature falls........ causes decrease in temperature.e.g. ice....... when it freezes.... an exothermic reaction occurs and it solidifies...... as heat is given out and temperature of ice falls.

( Anybody correct me if am wrong )

 

[daredevil]

Re: Biology,Chemistry & Physics Help Available Here !



4.Water is a bad conductor as it is made up of covalent bonds in which the bonds are shared and all electrons are used up and therefore it does not allow for the conduction of electricity as electricity is conducted by electrons !

heyy i think u need some correction here.... water is not a bad CONduCTOR. in fact it is an veryyyy gud cnductor of electricity. it lets current pass easily. it is a bad ELECTROLYTE. so there's a difference. the point is that water does conduct electricity but it does not DISSOCIATE and if we recall what we read in the book: an electrolyte is a substance that dissociates into its ions when electricity is passed through it and if from physics lessons we recall the definition of a conductor it is a thing which "lets current flow through it"; there is no mention of dissociation. hope that this helps... gud luk

 

[fatikhalid]

can any 1 plz solve oct nov phy ppr 1 question 1 nd 6?? plzz