In 1819, French physicists Dulong and Petit found experimentally that for many s
ID: 1059058 • Letter: I
Question
In 1819, French physicists Dulong and Petit found experimentally that for many solids at room temperature, c 3R (R = gas constant in SI units). Show that Dulong-Petit's rule is in agreement with the specific heat capacities of metals in the table. Explain why the specific heat capacity of magnesium is roughly twice as large as the one of titanium, and why the specific heat capacities of lead and gold are nearly identical. Write the net ionic equation for the reaction between hydrochloric acid and aqueous sodium hydroxide reaction. How would the temperature change and the calculated heat of neutralization vary if the concentration of the acid and the base used in this experiment will double? Explain. In a coffee-cup calorimeter, 1.80 g of NH_4NO_3 is mixed with 74.0 g of water at an initial temperature of 25.00 degree C. After dissolution of the salt, the final temperature of the calorimeter contents is 23.07 degree C. Assuming the solution has a heat capacity of 4.18 J/g middot degree C and assuming no heat loss to the calorimeter, calculate the enthalpy change for the dissolution of NH_4NO_3 in units of kJ/mol.Explanation / Answer
3. Net ionic equation for the reaction between HCl and NaOH
H+(aq) + OH-(aq) ---> H2O(l)
4. For a coffee cup calorimeter
moles of NH4NO3 = 1.80/80.04 = 0.0225 mol
heat q = mCpdT
= 74 x 4.18 x (23.07 - 25)
= -596.9876 J
enthalpy change for dissolution dH = -596.9876/0.0225 x 1000
= -26.533 kJ/mol