ALL CIE CHEMISTRY DOUBTS HERE !!

[Deadly_king]

Nov 08 P4 No7(b)

Condensation reaction occurs between the NH₂ group of one amino acid and the CO₂H group of another amino acid to form a peptide linkage as described in the first picture.

However the questions ask about the formation about a tripeptide. Hence it will be a reaction involving 3 amino acids. The displayed formula of a tripeptide is shown in the second picture.

NOTE : The R groups of atoms may be replaced by almost any atom. However it will be much easier and simpler to replace it by H atom. Your answer should not consist of R.

[moon]

Thank u very much for ur reply as well as ur explanation. It is really helpful, but can u explain Q4(b)(iii), of the same year Nov. 2008? You have explained Q3 not Q4 and what is the formula of the tripeptide as shown in the markscheme?....I really do appreciate ur co-operation.

[Deadly_king]

Thank u very much for ur reply as well as ur explanation. It is really helpful, but can u explain Q4(b)(iii), of the same year Nov. 2008? You have explained Q3 not Q4 and what is the formula of the tripeptide as shown in the markscheme?....I really do appreciate ur co-operation.

Oops ....... sorry for the confusion dude.

4(b)(iii)

That will depend on the equation you wrote for part (b)(i).

Let's take it to be : C₈H₁₈ -----> 2C₂H₄ + C₄H₁₀
Now you need to find the enthalpy change for this reaction.

Number of bonds to be broken in the reactant : 18C-H bonds and 7C-C bonds.
Total number of bonds to be formed in the products : 2C=C bonds + 8C-H bonds and 3C-C bonds + 10C-H bonds.

Use the values from the Data Booklet to find :
(i) Energy required for bond-breaking : 18(410) + 7(350) = 9830 KJ/mol
(ii) Energy given out for bond formation : 2(610) + 8(410)  + 3(350) + 10(410) =  9650 KJ/mol

Standard enthalpy change of reaction : 9830 - 9650 = +180 KJ/mol

NOTE : Bond breaking is endothermic(+ve) while bond forming is exothermic(-ve).

Same method is applied whatever the equation you wrote in (b)(i).

(iv)

The conditions include a temperature of about 600^oC. Hence this suggests that the reaction is endothermic since heat must be supplied for the reaction to occur and this is confirmed by the entahlpy change obtained in (b)(iii).

7(b)
The formula of the tripeptide can vary. This is why the marking scheme only mentioned 'correct tripeptide'. The product in the second picture I uploaded earlier is the right answer. Except that it is asking for displayed formula, so you need to elaborate on the bonds and replace all the R groups by H for the simplest tripeptide.

[moon]

Thank you very much for ur help. I got it...

[Deadly_king]

Thank you very much for ur help. I got it...

You are welcome pal

[HUSH1994]

Anyone can answer this question urgently:
State the factors affecting the ionisation energy and state the action of each one of them

[Twinkle Charms]

Anyone can answer this question urgently:
State the factors affecting the ionisation energy and state the action of each one of them

1) Size of the positive nucleur charge -- as the atomic number increases, there is an increase in the nucleur charge which causes an increase in the ionisation energy.

2)Distance of the electron from the nucleus -- when the distance of electron increases from the nucleus, the attractive force decreases therefore ionisation energy decreases.

3)Shielding effect of the inner electrons -- all the electrons are negatively charged and repel each other. Electrons in filled inner shells repel electrons in the outer shell and reduce the effect of positive nucleur charge. This is called the sheilding effect. The greater the shielding effect on an electron, lower the ionisation energy.

[Arthur Bon Zavi]

1) Size of the positive nucleur charge -- as the atomic number increases, there is an increase in the nucleur charge which causes an increase in the ionisation energy.

2)Distance of the electron from the nucleus -- when the distance of electron increases from the nucleus, the attractive force decreases therefore ionisation energy decreases.

3)Shielding effect of the inner electrons -- all the electrons are negatively charged and repel each other. Electrons in filled inner shells repel electrons in the outer shell and reduce the effect of positive nucleur charge. This is called the sheilding effect. The greater the shielding effect on an electron, lower the ionisation energy.

  This!!

[Twinkle Charms]

This!!

You have to but in everything yeah? 

[Deadly_king]

1) Size of the positive nucleur charge -- as the atomic number increases, there is an increase in the nucleur charge which causes an increase in the ionisation energy.

2)Distance of the electron from the nucleus -- when the distance of electron increases from the nucleus, the attractive force decreases therefore ionisation energy decreases.

3)Shielding effect of the inner electrons -- all the electrons are negatively charged and repel each other. Electrons in filled inner shells repel electrons in the outer shell and reduce the effect of positive nucleur charge. This is called the sheilding effect. The greater the shielding effect on an electron, lower the ionisation energy.

rightly said Twinkle
+rep

[HUSH1994]

rightly said Twinkle
+rep

Thank You twinkle,+rep as well

[ruby92]

given that the bond energy needed to break an O2 bond is 150 what is thae standard enthalpy of atomisation?

[Deadly_king]

given that the bond energy needed to break an O2 bond is 150 what is thae standard enthalpy of atomisation?

According to your statement, when breaking the O² molecules, we get 2 oxygen atoms. For this 150KJ/mol energy is required. (Bond energy)

The definition of enthalpy change of atomisation :
It is the heat energy change when  one mole of separate gaseous atom of the element is formed from the element under standard state conditions.

By breaking the O₂ bond we obtain 2 moles of oxygen atom. But enthalpy change of atomisation requires only one mole of gaseous atom to be formed.

Hence the answer will be :150/2 = 75 KJ/mol

[Adzel]

Can someone plz answer these questions for me  ...

[nid404]

All of these? in a few hours.