Chemistry Question - Calorimetry?

I don't understand how to solve this problem:

When a 12.8g sample of KCl dissolves in 75.0g of water in a calorimeter, the temperature drops from 31.0°C to 21.6°C. Calculate the ∆H for the process:

KCl → K+ + Cl-

(The + and - in the K and Cl are superscripts.)

The equation to use is
q = m(SpHt)(delta T)

q is the amount of heat gained or lost = delta H for this process
m is the mass of the solution = 87.8g (12.8g + 75.0g)
delta T is the change in temperature during the process 31.0 oC - 21.6 oC = 9.4 oC
SpHt is the specific heat of the solution = 4.184 J / g oC
NOTE: Since the specific heat of the resulting KCl solution is not given, it will be assumed that it is the same as the specific heat of water.

q = (87.8g)(4.184J / g oC)(9.4 oC)
NOTE: Since the temperature is decreasing, it is an endothermic reaction so the values of q and delta H will be positive values.

q = +345J = delta H
q = mCdeltaT

C = specific heat of water - check your units, there is a C for oC and a C for Kelvin

delta T = change in temp - if you use the C that has oC then just subtract your temps! if Kelvin - convert!

m = mass

q at a constant pressure - which this is = delta H

The answers post by the user, for information only, does not guarantee the right.

More Questions and Answers:
  • 10 points!!!!?
  • What is the formula of peroxide of any ether? the coming oxygen atom ataches to which sight or atom of ether?
  • Need thermite?
  • Is Baking Powder or Baking Soda the substitute for Baby Powder?
  • Sodium acetate in a store?
  • Can you explain the phrase in chemistry "like dissolves like"? Polar dissolves with?
  • Paper chromatography question?
  • Science question.Help!?
  • Analysis of water for dissolved oxygen?