pls help! i need to know how to do this on a test!

Question

With a substance initially at 20.00 degree C, 5.00 g of solid sodium nitrate was dissolved in 100.0 g of water in a calorimeter, and the temperature of the resultant solution was 14.80 degree C. The specific heat of the aqueous solution was 4.20 J/g C, and the heat capacity of the calorimeter was 40.0 J/ C.

a. write a chemical equation for the dissolution of solid sodium nitrate in water
( is it 2NaNO3 (aq) + H2O --> 2HNO3 + Na2O or is it totally a different thing?)

b. was the dissolution of sodium nitrate in water endothermic, exothermic, neither, or cannot be determined? justify your choice
(is it endothermic? b/c your adding heat to dissolve it ? )

c. calculate the energy change per mole of sodium nitrate for dissolving solid sodium nitrate in water
i have no clue....

Answer 1

a) NaNo3 does not react with water instead it dissolves and  ionizes like (NaCl)

   

      NaNO3 -->  Na+  + NO3-

 

b) It is endothermic since the temperature decreases.

 

c)

 

the molecular weight of NaNO3 is 85g

 

The appropriate equation for the change in heat is q = m * c *(t2 - t1) 

where q is heat, m is the mass, c  is the specific heat and t is the temperature. 

So for the calorimetric measurement 

 

q = 5g * 4.20 J/(g C) * (20 - 14.8)C = 109.2 Joule

 

if 5g of material creates 109.2 Joule how much does 85g ?

 

85 g * 109.2J /5g =  1856.4 Joules