The determinant of a 2x2 matrix \( A = \begin{bmatrix} a & b \\ c & d \end{bmatrix} \) is calculated as \( ad - bc \). For the matrix \( A = \begin{bmatrix} 2 & 3 \\ 4 & 5 \end{bmatrix} \), the determinant is \( 2 \times 5 - 3 \times 4 \), which equals \( 10 - 12 = -2 \). The determinant of this matrix is therefore \( \boxed{-2} \).