ΔH0solution, of sodium nitrate (NaNO3) is 20.50 kJ/mol solute. Calculate quantity of heat that is absorbed if 50g sodium nitrate dissolves in 200g water. What is the change temperature of the water

Answer 1

molar mass NaNO3 = 84.99 g/mol

50 g NaNO3 x 1 mol / 84.99 g = 0.588 moles NaNO3

0.588 mol x 20.50 kJ/mol = 12.1 kJ of heat absorbed in dissolving 50 g NaNO3

To find the change in temperature of the water, we use q = mC∆T

q = heat = 12.1 kJ = 12,100 J

m = mass = 200 g of water

C = specific heat of water = 4.184 J/gº

∆T = change in temperature

Solving for ∆T, we have ...

∆T = q / (m)(C) = 21,100 J / (200 g)(4.184 J/gº)

∆T = -25.1ºC

This is the change in temperature and it has a negative sign since a positive ∆H of solution (+20.50 kJ/mol) indicates an endothermic reaction. This means heat is absorbed from the surroundings into the system, so the temperature of the surrounding would decrease and the temperature of the water would drop by 25.1ºC.