Sodium metal reacts with water to produce hydrogen gas and sodium hydroxide according to the chemical equation shown below. When 0.0 15 mol of Na is added to 100.00 g of water, the temperature of the resulting solution rises from 25.00 °C to 31.45 °C. If the specific heat of the solution is 4.18 J , calculate ΔH for the reaction, as written. 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) H= ?

Question

Quizplus · Accepted Answer

First, we need to calculate the amount of heat absorbed by the solution:

q = mcΔT

where q is the heat absorbed, m is the mass of the solution (100.00 g of water), c is the specific heat of the solution (4.18 J/g°C), and ΔT is the temperature change (31.45°C - 25.00°C = 6.45°C).

q = (100.00 g)(4.18 J/g°C)(6.45°C) = 2,729 J

Next, we need to convert the amount of heat absorbed to the amount of heat released by the reaction:

2,729 J = -ΔH

where ΔH is the enthalpy change of the reaction (in J/mol). We can convert J to kJ and mol to get the answer in kJ/mol:

-ΔH = -2.729 kJ = ΔH/n

where n is the number of moles of Na used in the reaction (0.015 mol). Solving for ΔH:

ΔH = -2.729 kJ/mol / 0.015 mol = -181.9 kJ/mol

Rounding to the correct number of significant figures gives us the final answer of -360 kJ (choice D).

Sodium Metal Reacts with Water to Produce Hydrogen Gas and Sodium