Edexcel CHEMISTRY DOUBTS!!!!

[elemis]

Show me some workings that you've done.

I want to see if you attempted this problem.

[Blizz_rb93]

Here's my work but idk if im right or no so i wanted to double check here

H2SO4 (l) + 2KCl (s) -> 2HCl (g) + K2SO4 (s)

Given that : H2SO4 (l) + 2KOH (s) -> K2SO4 (s) + 2H2O (l) ; enthalpy change = -342 kJ

and HCl (g) + KOH (s) -> KCl (s) + H2O (l) ; enthalpy change = -204 kJ

for the 2nd equation;
we put the products on the reactants side and the reactants on teh products sign
=> KCl (s) + H2O (l) -> HCl (g) + KOH (s)  and multiply each element by 2

=> 2KCl (s) + H2O (l) -> 2HCl (g) + 2KOH (s) ; so the enthalpy change right now is 204x2
the negative sign turns to positive as we reversed the equation


so the enthalpy change of reactoin wud be = -342 + (2x204) = 66kJ

i know that we wud have to multiply the 2nd reaction so that some parts of it wud be cancelled but im really confused=/ i just wanna know what are the STEPS we are required to know and how do we do these steps

Thank you

[Blizz_rb93]

Nevermind! I got it

[Blizz_rb93]

1)
a) C2H4 (g) + H2 (g) --> C2H6 (g)
The enthalpy change of this reaction can be found by experiment to be -136 kJ/mol. Calculate the enthalpy change using the mean bond enthalpies given in book.

C-C = 347 / C-H = 413 / C=C = 612 / H-H = 436

now here's my answer to this

1 x (C=C) + 4 x (C-H) + 1 x (H-H) -> (612) + (4 x 413) + (436) = 2700

now for the products side -> 6 x (C-H) + 1 x (C-C) = 2825

2700 - 2825 = -125 kJ/mol ; exothermic reaction

so is that right? i just wanna doublecheck here

now for b)
The values will be different, why is this??

I was assuming it could be due to some experimental errors or heat loss ? is that right? either way what would your answer be?


Thank you! =)

[elemis]

1)
a) C2H4 (g) + H2 (g) --> C2H6 (g)
The enthalpy change of this reaction can be found by experiment to be -136 kJ/mol. Calculate the enthalpy change using the mean bond enthalpies given in book.

C-C = 347 / C-H = 413 / C=C = 612 / H-H = 436

now here's my answer to this

1 x (C=C) + 4 x (C-H) + 1 x (H-H) -> (612) + (4 x 413) + (436) = 2700

now for the products side -> 6 x (C-H) + 1 x (C-C) = 2825

2700 - 2825 = -125 kJ/mol ; exothermic reaction

so is that right? i just wanna doublecheck here

now for b)
The values will be different, why is this??

I was assuming it could be due to some experimental errors or heat loss ? is that right? either way what would your answer be?


Thank you! =)

Yeah, your method is correct and so is your calculation.

However, for the b part you are wrong. The data booklet quotes MEAN bond enthalpies. That is, they have found the average bond eenrgy for C-H bond.

Thus, the actual value of the C-H bond in ethene or ethane might be differ from the MEAN bond energy.

This why there is a difference.

[Blizz_rb93]

Thank you !
+rep

[Blizz_rb93]

1. Name and write out the full structural formulae for the following compounds :
a) CH3(CH2)2Cl

b) CH3C(CH3)2CH(CH3)CH3

:S i really dont know how to write it down
when the (CH2)2 does that mean that theres two CH2 branches ??

and can someone show me the answers of both so i can double check my work?

[Shazizzzle]

1. Name and write out the full structural formulae for the following compounds :
a) CH3(CH2)2Cl

b) CH3C(CH3)2CH(CH3)CH3

:S i really dont know how to write it down
when the (CH2)2 does that mean that theres two CH2 branches ??

and can someone show me the answers of both so i can double check my work?

Yes, the (CH2)2 means there are two CH2.
See the image attached. I've written both the structural formula, as well as the displayed one, for better understanding.

[Blizz_rb93]

Yes, the (CH2)2 means there are two CH2.
See the image attached. I've written both the structural formula, as well as the displayed one, for better understanding.

Thank you =)

[Shazizzzle]

Where can I get the answers to the Examzone Unit 2 Test 1 for the Edexcel AS book?
I really need the answer to Q4 b) (iii) and (iv)on page 253 please, thanks.

[Aadeez || Zafar]

1. Name and write out the full structural formulae for the following compounds :
a) CH3(CH2)2Cl

b) CH3C(CH3)2CH(CH3)CH3

:S i really dont know how to write it down
when the (CH2)2 does that mean that theres two CH2 branches ??

and can someone show me the answers of both so i can double check my work?

(CH2) means R---CH2--CH2----R
FOR EXAMPLE : -CH3(CH2)5CHClCH3

WOULD MEAN

CH3----CH2----CH2----CH2----CH2----CH2--CHCl--CH3

naming - 2-chloro-octane

[Aadeez || Zafar]

Thank you =)

if still any problem

then watch videos of khanadcademey.org (ORGANIC CHEMISTRY PLAYLIST)
u know it perfectly

[EMO123]

if still any problem

then watch videos of khanadcademey.org (ORGANIC CHEMISTRY PLAYLIST)
u know it perfectly

khan academy has got many more videos also so watch it all of chemistry also

[Blizz_rb93]

Explain why the different fractions of crude oil are collected at different temperatures?

[Master_Key]

Explain why the different fractions of crude oil are collected at different temperatures?

The chains of hydrocarbon are of different lengths so they have different boiling points and thus are separated at different temperatures.