A styrofoam cup calorimeter is used to determine the heat of reaction for the dissolution of an ionic compound in water. When 3.70 g of this compound is added to 500.0 mL of water, the temperature drops from 22.8°C to 16.3°C. Calculate the heat of reaction (qrxn = ΔHrxn) per gram of compound (in kJ/g).

So... Where do I begin?

Question

A styrofoam cup calorimeter is used to determine the heat of reaction for the dissolution of an ionic compound in water. When 3.70 g of this compound is added to 500.0 mL of water, the temperature drops from 22.8°C to 16.3°C. Calculate the heat of reaction (qrxn = ΔHrxn) per gram of compound (in kJ/g). 

So... Where do I begin?

anonymous · Answer

This is based on the amount of energy needed to make the temperature of the water increase by a certain amount. This is termed the specific heat capacity and for liquid water this is 4.1813 J per gram per degree kelvin. It would be the same for degrees centigrade too of course.  I think the difference in temp is 4.5 degrees and so the reaction required 4.5 x 4.1813 x 500 Joules. Divide this by the number of grams of the compound and convert to kJ and you'll have the answer. Post what you think it is and I'll check it if you like

anonymous · Answer

Well, I think the temperature change is 6.5, so would the final answer be 3.671621 kJ/mol?

anonymous · Answer

Wait, I tried it. It's totally right!! Thank you so  much.

anonymous · Answer

It's a good job you can count better than me! I'm glad you got the hang of it. Best wishes,