Teacher told us that the concentration term for pure liquids and solids is always $1$. But online I found this reaction:
$$\ce{CH3COOH(l) + CH3CH2OH(l) <=> CH3COOCH2CH3(l) + H2O(l)}$$
According to this page on LibreTexts (search for "esterification" to quickly find it),
$$K_c = \frac{[\ce{CH3COOCH2CH3}][\ce{H2O}]}{[\ce{CH3COOH}][\ce{CH3CH2OH}]}$$
Shouldn't $K_c = 1$ as all reactants and products are liquids? The above expression even contains $[\ce{H2O}]$.