Problem 21 - Chemistry An Atoms First Approach

Question

When pure methanol is mixed with water, the resulting solution feels warm. Would you expect this solution to be ideal? Explain.

Step-by-Step Solution

Answer

No, the methanol-water solution is not ideal because it feels warm when mixed, indicating that there is an energy change and a non-zero enthalpy of mixing (ΔH_mix). In an ideal solution, the enthalpy of mixing should be equal to zero, and no energy change should occur during the mixing process.

Step 1: Understanding Ideal Solutions

An ideal solution is a solution in which the interactions between the solute and solvent particles are the same as the interactions within the solute and solvent itself. There is no energy change when particles of different substances mix to form an ideal solution. This means that the enthalpy of mixing (ΔH_mix) is equal to zero. If the enthalpy of mixing is not equal to zero, then the solution is considered a non-ideal solution.

Step 2: Enthalpy and the given solution

In the given exercise, it is mentioned that the mixture of methanol and water feels warm. This means that heat is being released during the mixing process, and there is an energy change when methanol and water are mixed. This energy change is associated with the enthalpy of mixing (ΔH_mix). If heat is released, then the enthalpy of mixing is negative (exothermic process).

Step 3: Comparing with Ideal solutions

As mentioned earlier, for a solution to be considered ideal, the enthalpy of mixing (ΔH_mix) should be equal to zero. Given that the methanol-water solution feels warm (releasing heat) when mixed, its enthalpy of mixing is not equal to zero. Therefore, this solution is not an ideal solution.

Step 4: Conclusion

Based on the information given, the methanol and water solution releases heat when mixed, indicating an energy change and a non-zero enthalpy of mixing. As a result, this solution is not an ideal solution.