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hummi · Oct 19, 2010, 04:48 PM

Calculate the theoretical amount of CaCl2 that would be required to change the temperature of 50mL of water from room temperature 20deg.C to 45deg.C. Specific heat capacity of water is 4.184. The density of the water is 1g/mL.

Unknown008 · Oct 20, 2010, 09:25 AM

You need the enthalpy of solution of CaCl2 to solve this.

Then, you use $Q = mc\theta$

m = 50 g
c = 4.184 J/(gK)
theta = Final Temperature - Initial Temperature

Q is the required amount of energy.

Now, one mole of CaCl2 gives a certain amount of heat (the amount equal to the enthalpy of solution)
Find the number of moles required to match the amount of heat required.

Then, find its mass by first finding the relative mass of CaCl2.

Post what you get! :)

DrBob1 · Oct 21, 2010, 04:10 PM

I think you have a problem with your question. You have the heat capacity of water and Unknown008 shows you how to use it. BUT: the CaCl2 doesn't heat just the water. It has to heat itself too. It must take several grams (at least) of the salt to raise the solution temperature by 25 degrees. It is the total mass of the solution that has to be heated. When you look up the heat of solution of CaCl2 you have a new twist on that problem. If I recall correctly, heats of solution are measured on VERY dilute solutions to assure that the exotherm heats only the water. The data is said to be done at infinite dilution. So, Good Luck.