Monday

March 2, 2015

March 2, 2015

Posted by **redeye** on Thursday, March 7, 2013 at 3:09pm.

results 100.0ml of HCl with 0.31g of Mg ribbon temp before ribbon added 23degrees and after ribbon added 37degrees. Need to show work so I understand. q=mcdeltaT

- chem30 -
**DrBob222**, Thursday, March 7, 2013 at 3:22pmMg + 2HCl ==> H2 + MgCl2

q = mass H2O x specific heat H2O x (Tfinal-Tinitial)

q = 100 x 4.184 x (37-23) = ? for reaction.

q/g Mg = q/0.31g

If you want to convert to g/mol, then

(q/0.31)*atomic mass Mg = ?

Ususually these are quoted in kJ/mol; convert to kJ by dividing by 1000.

- chem30 -
**redeye**, Thursday, March 7, 2013 at 3:38pmso i use the specfic heat of water even thought its 100.0ml Of HCl solution that the Mg ribbon is going into. What is the units for the 100 if I do crossing off what do I end up with the deltaH should be in kj/mol

- chem30 -
**DrBob222**, Thursday, March 7, 2013 at 4:34pmThe problem didn't say it but usually solutions of acids are assumed to have the same specific heat as H2O (since most of the solution is H2O anyway). As for the mL thing, again most problems assume the density of dilute acid solutions (again, most of it is H2O) is 1.00 g/mL; therefore, 100 mL has a mass of 100 grams.

The units look like this.

100 g x 4.184 J/g*C x (37 C - 23C). The answer is in joules.

By the way, since it is delta H you want for kJ/mol Mg you must add a - sign to the answer. The water is there as a measuring stick for how much head is liberated by the reaction so the rxn liberates heat and the water absorbs it. q for the H2O comes out to be positive since it is absorbing the heat and that makes us add a - sign to q for the Mg rxn.

q/0.31 gives joules/gram.

(q/0.31g) x 24.3 g/mol gives J/mol and divide by 1000 to obtain kJ/mol Mg.

**Answer this Question**

**Related Questions**

math - There is a blue ribbon, a yellow ribbon, and a green ribbon. susan did ...

math - Mary bought a roll of ribbon.After using 5/8 of the ribbon to decorate ...

math word problem - Susan uses 15 rolls of ribbon to decorate 10 wedding baskets...

Math word problems - Susan uses 15 rolls of ribbon to decorate 10 wedding ...

math - Three friends each have some ribbon. Carol has 42 inches of ribbon, Tino ...

math word problem PLEASE HELP - Susan uses 15 rolls of ribbon to decorate 10 ...

math - if it takes 8 inches of ribbon to make a bow how many bows can be made ...

Fractions - The length of a ribbon is 3/4 meter. Tina needs pieces measuring 1/3...

Chemistry - When a student doesn't polish a sample of Mg ribbon before massing ...

fraction - Jenna bought a spool of ribbon for her craft projects.It contained 5 ...