When heat is added but the temperature remains constant, the sample would be in the process of changing phases.
\(T\) corresponds to the region when ethanol is a gas. \(R\) refers to the region when ethanol is a liquid.
The heat corresponds to temperature with the following equation:
$$ q = mc\Delta T $$
If constant heat is being applied but the temperature is increasing at a greater rate, it must mean that the \(c\) value (specific heat) is different for the the liquid and gas phases.
$$ q=mc\Delta T $$
$$ \frac{q}{m}=c\Delta T $$
$$ k = c\Delta T \text{ where } \frac{q}{m} \text{ is a constant}$$
If mass and heat are constant, the specific heat and temperature change are inversely related. Therefore a greater temperature change corresponds to a lower specific heat value and vice-versa.