How To Calculate The Temperature In Q = M*C (T2 - T1)?

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Offline carotis

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how to calculate the temperature in Q = m*C (T2 - T1)?
« on: May 26, 2016, 06:20:08 pm » So, perhaps someone could lend me a hand. :)It is the following question: I have 29,2 g of H2SO4 and mix it with water. It is an exotermic reaction. Which temperature has a H2O/H2SO4-mixture, when 29,2g of the H2SO4 is combined with 100g of water under 293,15 Kelvin. The heat capacity of this mixture is idealy 4,19 J / gK (it needn't hold onto reality, just assume it is the case <.< ) The Heat energy when dilutet with water is measured to be 95,33 KJ/molSo I know the formula Q = m*C (T2-T1), though I have nevr used it in calculations. Also despite the fact I have those given quantities, mass, heat, and heat capacity I just don't know if Q really is the given 95,33 Kj/mol because usually Q is desribed as Joule and not Joule per mole. Perhaps it is just a mishap on the behalf of the professor. So I used this formula and set it up this far: Q / (m*C = T2-T1 => Q / (m*C) + T1 = T2 So I have: 95330 J/mol / ( (29,2g+100g)*4,19J/g*K) + 293,15K = 469,24 KIs this calculation correct? Logged

Offline Borek

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Re: how to calculate the temperature in Q = m*C (T2 - T1)?
« Reply #1 on: May 27, 2016, 02:59:55 am » Quote from: carotis on May 26, 2016, 06:20:08 pm
I just don't know if Q really is the given 95,33 Kj/mol because usually Q is desribed as Joule and not Joule per mole.
Hard to say. If it is per mole it can also be so called specific dilution heat, which would be produced when exactly 1 mole of the acid is diluted.Your calculation is - in general - OK (but can be wrong if the number given is the specific heat). Just watch your significant figures. Logged Chembuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline mjc123

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Re: how to calculate the temperature in Q = m*C (T2 - T1)?
« Reply #2 on: May 27, 2016, 04:27:15 am » "Specific" usually means "per unit mass", so the specific dilution heat would be in J/g.If you have the molar heat of dilution in kJ/mol, you need to work out how many moles of H2SO4 you have, and calculate Q (in J) accordingly.You know your calculation must be wrong because the units are wrong - your "Q/mC" has units of K/mol instead of K. Logged

Offline carotis

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Re: how to calculate the temperature in Q = m*C (T2 - T1)?
« Reply #3 on: May 27, 2016, 04:48:04 am » exactly... so first n = m/M for sulfur acid => 29,2g/98g/molThen the Heat Energy, I just call it reaktion enthalpy times n => 95330 J/mol * n mol => Q (in Joule) Then: deltaT = Q/(m*C) The result is then the result of the calculation plus the 293,15 K, correct me if I'm wrong. :)The thing is, this is stupid online test, and everytime you are wrong you have to calculate all over again because the mass of H2SO4 allways changes, and that's quite annyoing after like 10 times you have to watch the same video again and calculate,calculate,... so just want to be sure if my problems lie in mathematics or the other 2 questions were wrong answered >:( Logged

Offline carotis

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Re: how to calculate the temperature in Q = m*C (T2 - T1)?
« Reply #4 on: May 27, 2016, 11:33:06 am » seriously though, it would be a blast weh nI just could post my concerns here, it would spare me much more time perparing for, I don't want to name it... EXAMS! How do we suppose to pass them when they make so much trouble with those stupid online tests.. Logged
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