Enthalpy Changes

Question

50.0mL of 0.500 mol/L of Copper (II) sulfate solution is mixed with 50.0mL of 1.00 mol/L solution of sodium hydroxide in a coffee-cup calorimeter. The temperature change is recorded to be 5.32°C

a. What is the enthalpy change for the reaction?

b. Write the thermochemical equation.

Answer 1

Assuming that the density of both solutions is 1 g/ml, we can estimate the mass of each and we will also assume that the specific heat of both solutions is that of water, i.e. 4.184 J/gº. Finally, we'll assume that the mass of copper sulfate and sodium hydroxide is negligible compared to that of the total solution. A lot of assumptions, I know, but just covering all bases.

q = mC∆T

q = heat = ?

m = mass = 50 ml + 50 ml = 100 ml x 1 g/ml = 100 g

C = specific heat = 4.184 J/gº

∆T = change in temperature = 5.32º

a). q = (100 g)(4.184 J/gº)(5.32º) = 2226 J = ∆H_rxn

0.050 L x 0.5 mol/L = 0.025 moles CuSO4

0.050 L x 1.0 mol/L = 0.050 moles NaOH

∆H/mole = 2226 J/0.025 = 89,040 J/mol = 89.0 kJ/mol

b) CuSO₄(aq) + 2NaOH(aq) +89.0 kJ ==> Cu(OH)₂(s) + Na₂SO₄(aq)

or CuSO₄(aq) + 2NaOH(aq) ==> Cu(OH)₂(s) + Na₂SO₄(aq) ∆H = +89.0 kJ/mol