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Theloshua
 one year ago
If 30.0 mL of 0.150 M aqueous sodium hydroxide is mixed with 30.0 mL of 0.150 M aqueous hydrochloric acid in a calorimeter at an initial temperature of 25.0 degrees Celsius, what is the enthalpy change of this reaction if the final temperature reached in the calorimeter is 27.5 degrees Celsius?
NaOH + HCl yields NaCl + H2O
Theloshua
 one year ago
If 30.0 mL of 0.150 M aqueous sodium hydroxide is mixed with 30.0 mL of 0.150 M aqueous hydrochloric acid in a calorimeter at an initial temperature of 25.0 degrees Celsius, what is the enthalpy change of this reaction if the final temperature reached in the calorimeter is 27.5 degrees Celsius? NaOH + HCl yields NaCl + H2O

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aaronq
 one year ago
Best ResponseYou've already chosen the best response.1For calorimetry reactions, use the equation: \(q=m_{water}*C_p*\Delta T\) where m is the mass of water (or solution in this case) Cp is the specific heat capacity for the system (i would assume it to be the same as water here) \(\Delta T\) is change in temperature the system underwent

aaronq
 one year ago
Best ResponseYou've already chosen the best response.1oh yea and q is the heat evolved (which is equal to the change in enthalpy under constant pressure, which I assume it's valid here)

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0okayy..... so..... wait

aaronq
 one year ago
Best ResponseYou've already chosen the best response.1lol so \(C_p=4.18 ~J/~ ^oC*g\) So we have \(\sf q=m*(4.18 ~J/~ ^oC*g)*(T_{final}T_{initial})\) we need the mass and the temperatures..

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0ummm.... but water isnt involved in the reaction...

aaronq
 one year ago
Best ResponseYou've already chosen the best response.1I know, but we're measuring the temperature of the water (solution), and that is how (indirectly) we're getting the change in enthalpy

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0but the solution isnt water XD so you dont know its heat capacity....

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0so isnt it irrelevant?

aaronq
 one year ago
Best ResponseYou've already chosen the best response.1It's common in these problems to make the simplification that the specific heat capacity is equal to that of water, unless you're told otherwise... same with the density of the solution, it's equal to that of water

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0okayy.... I hope your right... :p

aaronq
 one year ago
Best ResponseYou've already chosen the best response.1Unless you're told (in the question) otherwise, i'm right lol

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0so ummmm hold on let me plug in the equation

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0what is the mass of the equation? :/

aaronq
 one year ago
Best ResponseYou've already chosen the best response.1the mass of the solution, the density is assumed to be the same as water's so \(\sf mass=density*volume=1~g/mL*60~mL=60~g\)

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0im confused right now....

aaronq
 one year ago
Best ResponseYou've already chosen the best response.1What are you confused about?

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0you took the density and volume of water to find the mass right?

aaronq
 one year ago
Best ResponseYou've already chosen the best response.1yep, the definition for density is: \(\sf density=\dfrac{mass}{volume}\) so i just rearranged

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0but doesnt the density and volume of water depend on the amount? or no?

aaronq
 one year ago
Best ResponseYou've already chosen the best response.1the density depends on a lot of things, most importantly temperature. Again, these problems make the simplification that the density of the solution is the same as that of water .. which is further simplified and rounded to 1 g/mL. The volume is given in the question

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0oh, you added the two volumes?

aaronq
 one year ago
Best ResponseYou've already chosen the best response.1Thats the volume of the solution

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0okayyyy so \[Q = 60 \times 4.18 \times (27.5  25)\]

aaronq
 one year ago
Best ResponseYou've already chosen the best response.1yep. theres one final thing, because this is the energy absorbed by the water it is an endothermic process, but the reaction is exothermic as energy was released. \(\sf q_{absorbed}=q_{released}\) you need to change the sign

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0oh okay, but what about the values given (0.250 M)?

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0where do those come in?

aaronq
 one year ago
Best ResponseYou've already chosen the best response.1they don't, unless they want the molar enthalpy of the reaction. You'll come across questions that include more info than you need and you have to know what to use and what is irrelevant

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0The answer would be 627?

aaronq
 one year ago
Best ResponseYou've already chosen the best response.1yep, just tack on some units to that

Theloshua
 one year ago
Best ResponseYou've already chosen the best response.0okay, thnx so much!!!!
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