Question

Magnesium metal reacts with acid in solution according to the following reaction:

Mg(s)+2H+(aq)→Mg2+(aq)+H2(g)

When 0.1021 g of Mg(s) is combined with enough acid solution to make 150.0 g of solution in a coffee-cup calorimeter, all of the magnesium reacts, raising the temperature from 21.80 ∘C to 24.90 ∘C. Assume that the solution is mostly water, so that the heat capacity is 4.184 J⋅g−1⋅∘C−1.

1) Determine ΔrH for the reaction (at 298 K).

2)Determine ΔrU for the reaction (at 298 K)

Hi, I am struggling to solve this question. Please help me solve it. Thanks.

Answer 1

Hi Aqeela!

Expert-Verified Answer

Answer:

To determine ΔrH for the reaction, use the equation: ΔH = q_p / n, where q_p is the heat absorbed by the solution and n is the number of moles of the reactant.

First, find the heat absorbed by the solution: q_p = m_s * c_s * ΔT = 150 g * 4.184 J/g/°C * (24.90 °C - 21.80 °C) = 1162.72 J.

Next, find the number of moles of magnesium: n = m / M = 0.1021 g / 24.31 g/mol = 0.00418 mol.

Finally, ΔrH = ΔH / n = 1162.72 J / 0.00418 mol = 276,375 J/mol.

To determine ΔrU for the reaction, use the equation: ΔU = ΔH - TΔS, where ΔS is the entropy change and T is the temperature in kelvin.

Since ΔS is not given, we cannot determine ΔrU.