Chem Quiz #7

1. (15 pt.) The following acid/base reaction occurs at 298 K and 1 atm of pressure:

H₂SO_{4 (aq)} + 2 NaOH _(aq) Y Na₂SO_{4 (aq)} + 2 H₂O _(l)

100.0 mL of 1.0 M H₂SO₄ is added to 100.0 mL of 1.0 M NaOH in a coffee cup calorimeter. The initial temperature of both solutions is 25ºC. After mixing for several minutes, the temperature peaks at 29.4ºC. Assuming the density of the solutions is approximately that of water, 1.0 g/mL, and the specific heat is also approximately that of water, 4.18 J/gºC, what is the )Hº_rxn in kJ?

200.0 mL of solutions * 1 g/mL = 200.0 g of solutions

q = mc)T = 200.0 g * 4.18 J/gºC * (29.4 ºC – 25.0 ºC)

q = 3678 J = 3.678 kJ

q_rxn = - q_calorimeter

q_rxn = -3.678 kJ

)H_rxn = -3.678 kJ – This is specific to the quantities of reactions actually used, )Hº_rxn is independent of the actual amount used.

Find the limiting reagent and the actual amounts that react:

1.0 M H₂SO₄ * 0.100 L = 0.1 mol H₂SO₄ * (1 mol Na₂SO₄/1 mol H₂SO₄) = 0.1 mol Na₂SO₄

1.0 M NaOH * 0.100 L = 0.1 mol NaOH * (1 mol Na₂SO₄/2 mol NaOH) = 0.05 mol Na₂SO₄

)Hº_rxn = -3.678 kJ * 1 mol Na₂SO₄ = -73.56 kJ

0.05 mol Na₂SO₄