Chemistry Questions (1 Viewer)

[Immortalp00n]

Re: Quick question

Hey Aysce,

How's uni going cuz,


the question is pretty simply, I took this from my notes today, see if it helps your.

See from the Periodic Table that Iodine has atomic number 53, so the proton: neatron ratio is 53: 67. so you can see that atomic no. is less than less than 83, so it is considered as a stable isotope.

• A stable isotope’s nucleus doesn’t change
• A radioactive isotope has an unstable nucleus which releases particles/energy to become more stable.
o Any isotope with atomic number > 83, is unstable
o Stability of nucleus also depends on neutron-to-proton ratio.
o Most stable nuclei are found in an area of graph known as the ‘zone of stability’
• Radioactivity is the spontaneous change in composition of an unstable nucleus leading to the emission of radiation.

• Alpha-decay
o Occurs when there are too many protons AND neutrons (nucleus too heavy).


• Beta-decay
o Occurs when there are too many neutrons for the # of protons present. A neutron turns into a proton and electron
o Mass number remains same, atomic number +1, electron emitted.


• Positron emission
o Occurs when there are too many protons for the # of neutrons present. A proton becomes a neutron and positron
o Mass number remains same, atomic number -1, positron emitted.


• Electron capture
Occurs when there are too many protons for the no. of neutrons present. An inner-orbital electron is captured by the nucleus, converting a proton into a neutron.

• Gamma radiation
o Emission of high energy photons enables nucleus to lose excess energy and become more stable

yes peters is absolutely right, also check my above notes!

I am currently in year 12, aiming for medicine too lol.

Great explanation bro!

 

[Aysce]

Re: Quick question

Hey Aysce,

How's uni going cuz,


the question is pretty simply, I took this from my notes today, see if it helps your.

See from the Periodic Table that Iodine has atomic number 53, so the proton: neatron ratio is 53: 67. so you can see that atomic no. is less than less than 83, so it is considered as a stable isotope.

• A stable isotope’s nucleus doesn’t change
• A radioactive isotope has an unstable nucleus which releases particles/energy to become more stable.
o Any isotope with atomic number > 83, is unstable
o Stability of nucleus also depends on neutron-to-proton ratio.
o Most stable nuclei are found in an area of graph known as the ‘zone of stability’
• Radioactivity is the spontaneous change in composition of an unstable nucleus leading to the emission of radiation.

• Alpha-decay
o Occurs when there are too many protons AND neutrons (nucleus too heavy).


• Beta-decay
o Occurs when there are too many neutrons for the # of protons present. A neutron turns into a proton and electron
o Mass number remains same, atomic number +1, electron emitted.


• Positron emission
o Occurs when there are too many protons for the # of neutrons present. A proton becomes a neutron and positron
o Mass number remains same, atomic number -1, positron emitted.


• Electron capture
Occurs when there are too many protons for the no. of neutrons present. An inner-orbital electron is captured by the nucleus, converting a proton into a neutron.

• Gamma radiation
o Emission of high energy photons enables nucleus to lose excess energy and become more stable

yes peters is absolutely right, also check my above notes!

I am currently in year 12, aiming for medicine too lol.

Thanks Omed - haven't started yet haha.

Where did you get this information from? It isn't from the textbook and certainly isn't in the state ranking notes I have.

 

[someth1ng]

Re: Quick question

Omed62's explanation is pretty similar to what's in my notes.

 

[Aysce]

Re: Quick question

Omed62's explanation is pretty similar to what's in my notes.

Where did you source this info from? Strange how this isn't in the notes im using (they're fairly reliable too)

I only have the basic alpha and beta decay but nothing else.

 

[Immortalp00n]

Re: Quick question

Omed62's explanation is pretty similar to what's in my notes.

Lmao does pretty similar = same thing?

 

[Peter-PF7]

Re: Quick question

Yeh Omed62's info is same as mine... i didnt get it from a textbook, our chem teacher went through each form of radiation with us in class and clarified with a US documentary...

 

[Aysce]

Re: Quick question

Yeh Omed62's info is same as mine... i didnt get it from a textbook, our chem teacher went through each form of radiation with us in class and clarified with a US documentary...

Figures why I don't know it lol. Thanks!

 

[Aysce]

Le Chatelier Question

I'm a little uncertain about this question since there are no answers in the textbook and just want to confirm my answer.

http://imageshack.us/photo/my-images/820/screenshot20130131at720.png/

 

[RishadM]

Re: Le Chatelier Question

It's endothermic because if you were to write "+heat/energy", you would have to write it on the left side. This is because adding heat to the solid makes it dissolve and form the right side.

 

[Aysce]

Re: Le Chatelier Question

Still a little unsure :/

 

[mac1996]

Re: Le Chatelier Question

Le Chatelier's principle states that if a system at equilibrium is disturbed, then the system adjusts itself so as to minimise the disturbance. As the temperature increases the system will move to the left, increasing the concentration of nitrate and potassium ions. The solubility of KNO3 will therefore increase as the system will shift to the left, thus minimising disturbance and absorbing the increase in heat.

Im pretty sure its the right answer. Hope it helps

 

[Aysce]

Re: Le Chatelier Question

Le Chatelier's principle states that if a system at equilibrium is disturbed, then the system adjusts itself so as to minimise the disturbance. As the temperature increases the system will move to the right, increasing the concentration of nitrate and potassium ions. The solubility of KNO3 will therefore increase as the system will shift to the left, thus minimising disturbance and absorbing the increase in heat.

Im pretty sure its the right answer. Hope it helps

How do you know as temperature increases, the system moves right? You don't know if the forward reaction is endothermic or not?

Sorry im just getting muddled up

 

[golgo13]

Re: Le Chatelier Question

I would say that you are providing energy to break down the solid kno3 (disturbing the equilibrium), similarly you can think of saturated solution of sucrose water, but when heat is applied you are able to super saturate the solution

"Forgot second part"
As for that it is endothermic, because by providing energy you are forcing a forward reaction (to the right), as opposed to the left (exothermic in this case)

 

[Aysce]

Re: Le Chatelier Question

The thing is, I keep getting confused with the forward reaction being exothermic because since it releases heat, it increases temperature and hence KNO3 becomes more soluble. Can you just like explain to me what's wrong with this statement?

 

[golgo13]

Re: Le Chatelier Question

I think what you have to do is keep it in simple terms, the idea of the question is to test your ability to interpret the data given. For all you know they can change the chemicals used to play against rote learn. As a general rule of thumb when EQ moves to the right it's a forward reaction. Forward reaction is desirable in most of the questions you'll face
If EQ moves to the left it's a reverse reaction. The idea of exothermic and endothermic is to imply how the substance responds.
So in this instance i've applied energy and gotten a forward reaction, i would imply that it is endothermic, because it has responded to a desirable direction. However if it shifted to the left (revers direction). Then i would imply it is exothermic, because by adding heat i'm hindering my desired product.
Hope that helps

 

[LoveHateSchool]

Re: Le Chatelier Question

So the question states that "the solubility of KNO3 increases as temperature increases". This tells that "+heat" goes on the LHS of the equation, as you know heat helps in the dissolution of the solid.

So it will be KNO3(s) + heat ----> K+(aq) + No3-(aq) with a postive deltaH value as per endothermic reactions.

As such, I then approach Le Chatelier's Principle more easily as I can visually see what will happen, and what adding heat will do to the equation. Because adding something to the equation, I see it as pushing/pulling along the top and bottom arrow. This is known as shifting right, it literally favours the reaction pointing to the right.

*If more heat is added, the system will favour the forward reaction increasing concentration of potassium and nitrate, to minimize disturbance of added heat.
*If heat is removed from the system, the backwards reaction is favoured, and the concentration of KNO3 will increase. It literally favours the reaction arrow pointing to the left, hence lying more on the left.

 

[Aysce]

Re: Le Chatelier Question

Thanks a lot LHS, now I just need to clarify this and only this: So as temperature increases, the solubility of KNO3 increases as well. Although, through an endothermic reaction occurring, aren't we actually decreasing the overall temperature of this reaction since heat is being absorbed rather than released?

 

[LoveHateSchool]

Re: Le Chatelier Question

Thanks a lot LHS, now I just need to clarify this and only this: So as temperature increases, the solubility of KNO3 increases as well. Although, through an endothermic reaction occurring, aren't we actually decreasing the overall temperature of this reaction since heat is being absorbed rather than released?

When temperature increases, it is absorbed to overcome the covalent bonds of the solid to form ions. Delta H is positive as endothermic reaction occurs when the temperature of an isolated system decreases. What exactly do you mean by overall?

My advice with anything with Le Chatelier's is always stick determine what side +heat needs to go on, because it makes the questions much more friendly to tackle.

 

[Aysce]

Re: Le Chatelier Question

When temperature increases, it is absorbed to overcome the covalent bonds of the solid to form ions. Delta H is positive as endothermic reaction occurs when the temperature of an isolated system decreases. What exactly do you mean by overall?

My advice with anything with Le Chatelier's is always stick determine what side +heat needs to go on, because it makes the questions much more friendly to tackle.

Oh wait: So the temperature is increasing and due to this more of the KNO3 is being ionised. To maintain equilibrium, the forward reaction must be endothermic? :s

Disregard "overall", my bad.

 

[HKspec009]

Re: Le Chatelier Question

To produce more soluble potassium nitrate when heat increases, heat has to be on the left. When you add heat, for the system to minimise the disturbance it will shift it to the right producing more soluble KNO3.
Also iirc, heat increases rate not yield :S