general chem chapter 6

Question

When 0.374 g of sodium metal is added to an excess of hydrochloric acid, 3890 J of heat are produced. What is the enthalpy of the reaction as written?

2Na(s)+2HCl(aq) ----- 2NaCl(aq)+H2(g)

Answer 1

Hello, Sarah,

I'll assume the units of enthalpy desired are kJ/mole. Some are also reported as kJ per unit mass, such as kg.

The heat produced is 3.890 kJ. Since it is released from the system, we add a negative sign in front, for -3.890kJ.

Convert 0.374 grams sodium into moles of sodium by dividing by sodium's molar mass of 32 g/mole. That is only 0.0163 moles of Na. Divide that into the total energy released to yield -238.65kj/mole enthalpy. Make that -238kJ/mole for 3 sig figs.

Bob