Chem Help?!?

Question

Two questions:
1. calculate the expected change in temperature for 4.5 g of NH4NO3 dissolved in 100.0 mL of H20. Assume that the calorimeter absorbs no heat. (ie. Ccal=0)

2. Calculate the change in temperature for 4.50 g of CaCl2 dissolved in 90.0 mL of H20. Assume that the calorimeter absorbs no heat (ie. Ccal=0)

Answer 1

In order to solve either of these problems, you're going to need to find the DH for dissolving both of those two compounds. I'm guessing that they're in a table in your text or in a previous problem...

Once you have those values, see what their units are. They might be Joules/gram, calories/gram, Joules/mole or calories/mol.

If they are either of the first two, you can multiply the mass of the substance by that value. That will give you the amount of heat absorbed when NH4NO3 dissolves or the amount of heat released when CaCl2 dissolves.

If they are given in Joules/mol or calories/mol, you'll need to convert the masses of each substance into moles by dividing by their molar masses before you multiply them by the value.

In either case, you then know the amount of heat absorbed or released. Then, you'll use the equation:

q = m c DT (I can't type a delta), where m is the volume of the water, c is the specific heat of water and q is the amount of heat gained or released that you calculated.

Hope this helps you...