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# OCR B (Salters) Chemistry F331 (Chemistry for Life) Thursday 23rd May Exam Discussion watch

1. What's the equation for the calorimeter test...temp change x ....
2. (Original post by Maishaashraf)
You write that endothermic takes in energy from the surrounding and is deltaH+ and is bond breaking
exothermic gives out energy to the surroundings and is deltaH- and is bond forming, therefore more energy is being released than taken in. There is a higher value for exothermic than endothermic
No

See 1aiii in

That kind on question
3. Look at the unfair MS for it
4. (Original post by Maishaashraf)
What's the equation for the calorimeter test...temp change x ....
Q=m*c*delta t

Where M is the mass of water being heated..
C is the specific heat capacity of water, usually 4.18 (given in the question)
Delta t is the change in temperature of water (final temperature of water - start temperature)

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5. E=mcdeltaT

Energy transferred to water=mass of water x specific heat capacity of water x temperature change

Btw g=cm3 so volume of water in cm3 is the SAME thing as mass of water in g.
6. (Original post by krisshP)
Say if you got isotopic masses with abundance
16-65%
17-35%

Ar of element=
(16 X 65)+(17 X35)

= 16.35
----------------------
100
I assume you mean 1635/100 = 16.35

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7. (Original post by krisshP)
No

See 1aiii in

That kind on question
Ohhhh sorry it's just incomplete combustion or losing fuel from the wick or heat loss to the surroundings
8. (Original post by Maishaashraf)
Oh basically what I do is draw the full structure of the equation and see how many bonds are being broken eg for the first one c3h8 there are 8 c-h bonds and 2 c-c bonds and you basically add up all the numbers using the table for the reactants and do the same with the products and you should come up with 2 different numbers. If its combustion just remember it has to be negative so take away highest number from the lowest number
No not that question

Look at 1aiii where it starts off by saying
A value for...
9. (Original post by Maishaashraf)
Ohhhh sorry it's just incomplete combustion or losing fuel from the wick or heat loss to the surroundings
See the MS
NOT evaporation from wick
10. And MS says that you can't you say standard conditions not used
11. (Original post by krisshP)
Look at the unfair MS for it
Can you post the mark scheme?
I assume its going to be, incomplete combustion of the fuel and heat energy escaping from the water via evaporation

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12. Holy ****
Somebody please remind me what reforming,isomerisation and cracking is?
I've got to go in 10 mins
13. (Original post by Iloveleonardo)
Holy ****
Somebody please remind me what reforming,isomerisation and cracking is?
I've got to go in 10 mins
Reforming increases octane number and is used to produce cycloalkanes and arenes with a higher octane number. Also produced is hydrogen in the process.

Isomerisation causes straight chain alkanes to convert into branched chain alkanes with a higher octane number.

Cracking uses long chain hydrocarbons which have high supply and low demand to convert them into shorter chain hydrocarbons which have low supply and high demand. The process produces alkenes, branched alkanes, shorter hydrocarbon molecules
14. (Original post by krisshP)
Reforming increases octane number and is used to produce cycloalkanes and arenes with a higher octane number. Also produced is hydrogen in the process.

Isomerisation causes straight chain alkanes to convert into branched chain alkanes with a higher octane number.

Cracking uses long chain hydrocarbons which have high supply and low demand to convert them into shorter chain hydrocarbons which have low supply and high demand. The process produces alkenes, branched alkanes, shorter hydrocarbon molecules
THANK YOU SO MUCH!
Good luck everybody
15. Exam starts in an hour. I shouldn't feel excited. Bleugh

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16. Last minute revision anyone?

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17. Will they ask any experimental questions

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18. How did everyone find it?

At the last minute saw my error on the last question - thank god I saw it xD

Jehearo

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19. omg yes could not have asked for a better exam

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