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# Q=mcT in a solution, which mass?

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1. Say you're mixing two aqueous compounds together, and they react in either an exo/endothermic reaction.
If a chemistry question tells you that c=4.2 kJkg^-1K^-1 but it doesn't tell you which solution this applies to, how do you know which mass to use in the equation Q=mcT to calculate the enthalpy change?
2. (Original post by Laurasaur)
Say you're mixing two aqueous compounds together, and they react in either an exo/endothermic reaction.
If a chemistry question tells you that c=4.2 kJkg^-1K^-1 but it doesn't tell you which solution this applies to, how do you know which mass to use in the equation Q=mcT to calculate the enthalpy change?
eyy it's quite common to get this wrong,

but m=mass of water
3. (Original post by thefatone)
eyy it's quite common to get this wrong,

but m=mass of water
Thank youuuu!

So would you use the total volume of water heated by the reactants, assuming 1cm^3 = 1g to work it out?

E.g. if you had 10cm^3 of aqueous "X" and 20cm^3 of aqueous "Y", the mass used in the equation is 30g?
4. (Original post by Laurasaur)
Thank youuuu!

So would you use the total volume of water heated by the reactants, assuming 1cm^3 = 1g to work it out?

E.g. if you had 10cm^3 of aqueous "X" and 20cm^3 of aqueous "Y", the mass used in the equation is 30g?
yes you would.

This brings me back to and hess's law..... oh the memories xD
5. (Original post by thefatone)
yes you would.

This brings me back to and hess's law..... oh the memories xD
You're a life saver, thanks! 1.7 years of a-level chemistry, and now I finally understand enthalpy
6. (Original post by Laurasaur)
You're a life saver, thanks! 1.7 years of a-level chemistry, and now I finally understand enthalpy
I'm so doomed for chem too i haven't revised enough bc i spend all my time on physics ._.
7. (Original post by thefatone)
I'm so doomed for chem too i haven't revised enough bc i spend all my time on physics ._.
I feel ya there, physics is intense.

Keep going, you can do it!!!!!!!
8. (Original post by Laurasaur)
I feel ya there, physics is intense.

Keep going, you can do it!!!!!!!
The only i can do is get a U >.> no matter how hard i try
9. (Original post by thefatone)
The only i can do is get a U >.> no matter how hard i try
I'm sending you some positive vibes
Don't give up, and anyway you've got a summer holiday to look forward to afterwards.
I would bake cake and cookies for you if I could, they make everything better!!
10. (Original post by Laurasaur)
I'm sending you some positive vibes
Don't give up, and anyway you've got a summer holiday to look forward to afterwards.
I would bake cake and cookies for you if I could, they make everything better!!
I know everyone irl and on here tres to make me positive but i will stay pessimist forever.

A summer holiday where i just work on A level stuff, find a job and searh for a course i wanna do at which uni(not fun.....)
11. (Original post by thefatone)
I know everyone irl and on here tres to make me positive but i will stay pessimist forever.

A summer holiday where i just work on A level stuff, find a job and searh for a course i wanna do at which uni(not fun.....)
Go outside and play with a puppy or something 😂
12. (Original post by Laurasaur)
Go outside and play with a puppy or something 😂
I know i'm being such a huge ****
but

I hate going outside and i don't want to do exercise. There is only more physics...
13. (Original post by thefatone)
I know i'm being such a huge ****
but

I hate going outside and i don't want to do exercise. There is only more physics...
Then I shall hunt you down and sushi you
14. (Original post by Laurasaur)
Then I shall hunt you down and sushi you
That fits so well with your avatar xD
Spoiler:
Show
i smiled a little like this

15. (Original post by thefatone)
That fits so well with your avatar xD
Spoiler:
Show
i smiled a little like this

Aww, any kind of smile will do
16. (Original post by Laurasaur)
Aww, any kind of smile will do
smile's from me are normal rarity
true meaning of the smile given though is a very different question
17. (Original post by thefatone)
smile's from me are normal rarity
true meaning of the smile given though is a very different question
Well, I do prefer certain smile-meanings...like rather than
18. (Original post by Laurasaur)
Aww, any kind of smile will do
you know you're sxcrewed for physics when you get 40% in a 2009 specimen paper.....
19. (Original post by Laurasaur)
Well, I do prefer certain smile-meanings...like rather than
LOL perv face xD
20. (Original post by thefatone)
you know you're sxcrewed for physics when you get 40% in a 2009 specimen paper.....
All I can say is to use the resources available to you. The textbook is okay, but physics videos are more interesting https://www.youtube.com/channel/UCZz...C-Dl_VVUVHYDYw

For past papers, are you going wrong on the maths or the wordy questions? If the answer is the maths, try using isaacphysics.org for practice. If it's the wordy stuff, go through the textbook for a better understanding, and use mark schemes to structure any notes (memorise the way they explain things).

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