Define an ideal solution.

Answer

### Step-by-Step Text Solution:

1. **Definition of Ideal Solution**: An ideal solution is defined as a solution in which the interactions between the molecules of the different components are similar to the interactions between the molecules of the same component.

2. **Components of an Ideal Solution**: Consider a solution made up of two components, A and B. In this solution, the interactions can be categorized as:
- AA interactions (between molecules of component A)
- BB interactions (between molecules of component B)
- AB interactions (between molecules of components A and B)

3. **Equality of Interactions**: For a solution to be classified as an ideal solution, the interaction between the molecules of different components (AB interactions) must be equal to the interactions between the molecules of each component:
\[ \text{AB interactions} = \text{AA interactions} = \text{BB interactions} \]

4. **Examples of Ideal Solutions**: A common example of an ideal solution is the mixture of n-hexane and n-heptane. These substances behave ideally when mixed together.

5. **Raoult's Law**: Ideal solutions obey Raoult's Law, which states that the partial vapor pressure of each component in the solution is directly proportional to its mole fraction in the solution.

6. **Enthalpy and Volume Changes**: In an ideal solution, the change in enthalpy (ΔH) upon mixing is equal to zero, and the change in volume (ΔV) upon mixing is also equal to zero:
\[ \Delta H_{\text{mixing}} = 0 \quad \text{and} \quad \Delta V_{\text{mixing}} = 0 \]