Edexcel CHEMISTRY DOUBTS!!!!

[Igcseboy]

6CH01 jan 2009 mcq 11 how to get to tht answer

thanxx

[vanibharutham]

Hydrogen and oxygen react according to the following equation.
2H₂(g) + O₂(g) ? 2H₂O(g)

If all volumes are measured at 110 °C and one atmosphere pressure, the volume of steam
produced after 50 cm³ of hydrogen react completely with 25 cm³ of oxygen is

A 25 cm³
B 50 cm³
C 75 cm³
D 100 cm³



AVOGADRO's LAW
"Equal volumes of ideal or perfect gases, at the same temperature and pressure, contain the same number of molecules."

At the given temperature and pressure,

1 mole = 25cm³
therefore,

the 2 moles of steam = 50cm³

[Igcseboy]

jan 2009 6CH01 question 24 c i and ii

[vanibharutham]

You prolly mean 24 d i) and ii)


d i) C₉H₂₀
ii) 3-ethyl-4-methylhexane

[Summer :]]

It's included in the syllabus. But in the A@ section; Unit 4.

I use the standardized edexcel book. It's included there, but not innthe syllabus.

Anyway, could anyone jot down a synopsis of IR Spectroscopy?

Thanks in advance.

Okay i find this site useful, check it out

http://www.chemguide.co.uk/analysismenu.html#top

[Meticulous]

Thanks. +rep.

[raimunts]

I've some doubts regarding "Dot AND Cross"/"Dot OR Cross" diagrams.
To show sharing of electrons in covalent compounds or transfer of electrons in ionic compounds which one should be used?
1. Dot AND Cross diagrams: This shows dots for electrons of one atom/ion and crosses for electrons of the other atom/ion. This way of showing electrons makes it very clear that the electrons from one atom is being transferred to another atom resulting in the formation of ions [ionic bonding] or showing that electrons from BOTH the atoms are being shared [covalent bonding.] The problem with this display method is written below.
2. Dot OR Cross diagrams: This shows ONLY either dots [dots for all electrons] or crosses [crosses for all electrons. This way is more scientifically accurate, because using two different types of symbols for electrons may imply that the electrons of different atoms are not the same, which is not true. If only dots or only crosses are used, then it is scientifically accurate because ALL electrons are the same.
Disadvantage of this method of display over the above one, is that showing BOTH dots and crosses makes it clear that electrons from both atoms are being shared.

So, which one should be used in the Edexcel AS Levels?
Thanx in advance for helping

[Meticulous]

You should use the dot AND cross diagram, in order to differentiate between electrons of different elements.

It's a MUST.

[raimunts]

Thanx Gladiator, I always use dot AND cross, but this friend of mine got me confused. You're sure about this tho, ryt?

[Meticulous]

Dead sure.

[Igcseboy]

You prolly mean 24 d i) and ii)


d i) C₉H₂₀
ii) 3-ethyl-4-methylhexane

no the question in which we have to find enthalpy change using mean bond enthalpy....

[Saladin]

no the question in which we have to find enthalpy change using mean bond enthalpy....

[Saladin]

Sorry, that should be 490.

[raimunts]

Speaking of enthalpy and stuff,
given there are 4 compunds A, B, C and D...and: A + B --> C + D
and standard enthalpy of formation/combustion is given for any three. Is it possible to find the remaining one from those three?
If it is, then what is the relationship?

[vanibharutham]

One element must be O₂ for it to be an enthalpy of combustion

in the attached file

1 = standard enthalpy of combustion of A
2 = standard enthalpy of formation of A
3 = standard enthalpy of formation of B
4 = standard enthalpy of formation of C

NB. O₂ does an enthalpy of formation of 0 kJ/mol

using Hess's Law

1 = 3 + 4 - 2

just substitute in the values