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# q=mcdeltaT A2 question

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1. So i was doing a past paper unit 5 aqa jun 13 and a Q=mcdeltaT question completely threw me off

"A solution is formed when 5.00 g of potassium chloride are dissolved in 20.0 g of water.The initial temperature of the water is 298 K.Calculate the final temperature of the solution.In your calculation, assume that only the 20.0 g of water changes in temperature andthat the specific heat capacity of water is 4.18 J K^–1 g^–1"

It was also previously given in the Q stem that the detaH solution of KCL is 17.2

to obtain the corrrect answer, it was necessary to realise that the "heat absorbed" i.e. 'q' in q=mcdeltaT, can be obtained by multiplying the deltaH solution of KCL by the number of moles of KCL (5/mr)

i competely and utterly do not understand why

any help much appreciated. thanks
2. (Original post by hi-zen-berg)
So i was doing a past paper unit 5 aqa jun 13 and a Q=mcdeltaT question completely threw me off

"A solution is formed when 5.00 g of potassium chloride are dissolved in 20.0 g of water.The initial temperature of the water is 298 K.Calculate the final temperature of the solution.In your calculation, assume that only the 20.0 g of water changes in temperature andthat the specific heat capacity of water is 4.18 J K^–1 g^–1"

It was also previously given in the Q stem that the detaH solution of KCL is 17.2

to obtain the corrrect answer, it was necessary to realise that the "heat absorbed" i.e. 'q' in q=mcdeltaT, can be obtained by multiplying the deltaH solution of KCL by the number of moles of KCL (5/mr)

i competely and utterly do not understand why

any help much appreciated. thanks
The energy per mol is obtained by dividing the energy change by the number of moles dissolved.
3. Hi hi-zen-berg

I find it hard to answer these questions by typing so please see the attached picture. It is x by moles because it is a rearrangement of the equation charco pointed out above.

I hope this helps!

Alex
4. (Original post by ajsullivan)
Hi hi-zen-berg

I find it hard to answer these questions by typing so please see the attached picture. It is x by moles because it is a rearrangement of the equation charco pointed out above.

I hope this helps!

Alex
YOU COMPLETE AND UTTER LEGEND!
this reallly really helped me visualize the Q and honed in on what i didnt get

thank you so, so much ajsullivan i hope you and your entire bloodline are forever blessed <3
5. (Original post by hi-zen-berg)
YOU COMPLETE AND UTTER LEGEND!
this reallly really helped me visualize the Q and honed in on what i didn't get

thank you so, so much ajsullivan i hope you and your entire bloodline are forever blessed <3
Wow that was a very nice thing to say!

You are very welcome - best of luck

Alex

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