Q=mcT in a solution, which mass?

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?

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Reply 1

thefatone

Original post by Laurasaur

eyy it's quite common to get this wrong,

but m=mass of water

Reply 2

Laurasaur

Original post by thefatone

eyy it's quite common to get this wrong,

but m=mass of water

Thank youuuu! :h:

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?

Reply 3

thefatone

Original post by Laurasaur

Thank youuuu! :h:

yes you would.

This brings me back to

k_c

and hess's law..... oh the memories xD

Reply 4

Laurasaur

Original post by thefatone

yes you would.

This brings me back to

k_c

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 :colondollar:

Reply 5

thefatone

Original post by Laurasaur

You're a life saver, thanks! 1.7 years of a-level chemistry, and now I finally understand enthalpy :colondollar:

I'm so doomed for chem too :cry:

i haven't revised enough bc i spend all my time on physics ._.

Reply 6

Laurasaur

Original post by thefatone

I'm so doomed for chem too :cry:

i haven't revised enough bc i spend all my time on physics ._.

I feel ya there, physics is intense. :ahhhhh:

Keep going, you can do it!!!!!!! :hugs:

Reply 7

thefatone

Original post by Laurasaur

I feel ya there, physics is intense. :ahhhhh:

Keep going, you can do it!!!!!!! :hugs:

The only i can do is get a U >.> no matter how hard i try

Reply 8

Laurasaur

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 :hippie:

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!!

Reply 9

thefatone

Original post by Laurasaur

I'm sending you some positive vibes :hippie:

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.....)

Reply 10

Laurasaur

Original post by thefatone

Go outside and play with a puppy or something 😂

Reply 11

thefatone

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...

Reply 12

Laurasaur

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 :h:

Reply 13

thefatone

Original post by Laurasaur

Then I shall hunt you down and sushi you :h:

That fits so well with your avatar xD

Spoiler

Reply 14

Laurasaur

Original post by thefatone

That fits so well with your avatar xD

Spoiler

Aww, any kind of smile will do :tongue:

Reply 15

thefatone

Original post by Laurasaur

Aww, any kind of smile will do :tongue:

smile's from me are normal rarity
true meaning of the smile given though is a very different question

Reply 16

Laurasaur

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 :grin:

rather than :perv:

Reply 17

thefatone

Original post by Laurasaur

Aww, any kind of smile will do :tongue:

you know you're sxcrewed for physics when you get 40% in a 2009 specimen paper.....

Reply 18

thefatone

Original post by Laurasaur

Well, I do prefer certain smile-meanings...like :grin:

rather than :perv:

LOL perv face xD

Reply 19

Laurasaur

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/UCZzatyx-xC-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).