can somebody explain how to work out enthalpy changes please?

  • 0 votes

i really do not understand how to work it out

Posted Wed 16th May, 2012 @ 14:29 by Danni

2 Answers

  • 3 votes

enthalpy change is all about energy changes. Normally heat.

The equation you need to remember is 'q = M C DeltaT'

Just think of it as a bad chemistry rapper - "Mc DeltaT"

M - Mass. Usually given to you in the equation. this is the mass of a substance that has been heated. 

C - Specific heat capacity - usually in the newer specs of most exam boards you will be asked to assume that the substance has the same capacity as water, which is 4.13 KJ mol-1.

Delta T - the change in temperature that has been measured.

Then you just place these into the equation and you get q.

For example, 

a 25.0CM3 sample of 2.00 mil dm-3 HCL was mixed with 50.0CM3 of a 1.00 mil dm-3 solution of NAOH. both solutions were initially at 18.00C. after mixing the temp. of the final solution was 26.5C.

Use this information to calculate the standard enthalpy change for the reaction.

SOOOO...

q = (25.0 + 50.0) x 4.13 x (26.5 - 18.0)

q = 2632.875 J Mol-1 OR 2.63 Kj Mol-1

Answered Wed 16th May, 2012 @ 15:53 by Daryl Ladd
  • 0 votes

thankyou , really helpful :)

Answered Thu 17th May, 2012 @ 16:25 by Danni