Deceitful Wing's question thread

[Deceitful Wings]

I am having trouble understanding polymer reactions.
How do you structure their chemical equations?
for example, if you had ethene, would it be:

-(C₂H₄)-_n --> -(C₂H₆)-_n

If it is, would it work the same way with any reactant to produce a polymer?
Thanks!

[Mao]

[Deceitful Wings]

VCAA 2010 Q. 3 a)
Write an equation showing how either an ethanol molecule or a nitrogen dioxide molecule becomes ionised in the mass spectrometer.

I put NO₂(g)-->NO₂⁺(g)+e^-

I don't understand why the assessment report says it's 2e^- though, can please someone explain why?

Thanks

[Mao]

I bet you the assessment report has:

[soccerboi]

I bet you the assessment report has:

Yeh just like in maths, we can simplify the eqn by cancelling an e on both sides to get NO2(g)-->NO2+(g)+e-, which is the same but a simplified version

Edit: Are you asking why they have this NO2(g)-->NO2+(g)+2e- ? I'm not sure about this one though...

[Lesliel1]

i THINK we don't simplify it because we need to show the bombarding e that knocks out an e on the molecule in order to ionise it in the ionisation chamber. Thus i there is one e in the reactant and 2e in the product.

i think thats what you asking?... maybe? haha

[Deceitful Wings]

yea that makes sense, thanks everyone!
>< I keep making silly mistakes like this, it's costing me marks in chem lol

Also with NMR, when you have a hydrogen atom next to a polar atom e.g. CH₃Cl, I don't understand how the hydrogen requires a greater chemical shift? if the hydrogen is more dieshielded due to electron density of the C-H bond being shifted away from the hydrogen atom, wouldn't that mean it requires a lower chemical shift? (hope that makes sense)

[soccerboi]

yea that makes sense, thanks everyone!
>< I keep making silly mistakes like this, it's costing me marks in chem lol

Also with NMR, when you have a hydrogen atom next to a polar atom e.g. CH₃Cl, I don't understand how the hydrogen requires a greater chemical shift? if the hydrogen is more dieshielded due to electron density of the C-H bond being shifted away from the hydrogen atom, wouldn't that mean it requires a lower chemical shift? (hope that makes sense)

Greater chemical shift means a weaker external magnetic field is required. in your example, the cl pulls electron density away from the carbon atom which itself pulls electron density from the H nucleus, so H nucleus is more exposed and less shielded. Becuase it's more exposed, it will require a weaker external magnetic field to achieve resonance, and this implies a higher chemical shift.

[aznxD]

The less the shielding the higher the chemical shift. As Chemical shift is 'inversely proportional' to the Magnetic Energy Level for Resonance. In other words if there is less shielding, less energy is required to reach resonance, hence the greater the chemical shift observed.

[Deceitful Wings]

With energy profiles, do they start at the a y-intercept? I am a bit confused as some study guides/resources have energy profiles starting at 0 (which doesn't make sense as reactants always must have chemical potential) whereas others studyguides/resources say that they do.

For example:
http://www.biologyreference.com/images/biol_02_img0148.jpg

http://www.chemguide.co.uk/physical/basicrates/profile.gif

If i was asked to draw an energy profile, what must i include so that i don't lose marks? I have a sac coming up on this, any help would be appreciated.

[Mao]

With energy profiles, do they start at the a y-intercept? I am a bit confused as some study guides/resources have energy profiles starting at 0 (which doesn't make sense as reactants always must have chemical potential) whereas others studyguides/resources say that they do.

They absolutely don't have to start at the axes origin. Chemical potential / enthalpy / whatever are all relative quantities. Some people choose to define their values relative to the standard enthalpies of formation, others choose other origins, it's really quite arbitrary.

[Deceitful Wings]

With energy profiles, do they start at the a y-intercept? I am a bit confused as some study guides/resources have energy profiles starting at 0 (which doesn't make sense as reactants always must have chemical potential) whereas others studyguides/resources say that they do.

They absolutely don't have to start at the axes origin. Chemical potential / enthalpy / whatever are all relative quantities. Some people choose to define their values relative to the standard enthalpies of formation, others choose other origins, it's really quite arbitrary.

Thanks Mao

I need help with another concept haha

Order the factors that provide a higher rate of reaction over the other (from the factor that would cause the highest increase in the rate of reaction to the least increase of the rate of reaction)
-Increased temperature
-Increased surface area
-Presence of a catalyst
-Increased concentration
-Increased radiation

Wouldn't this all be dependent on the strength of each factor? i.e. how high the temperature is, how much of reactant you added, how much catalyst is present?