18 At constant pressure, the change in which property of a system is equal to the energy flow as heat? (A)internal energy (B)work (C)entropy (D)Gibbs free energy (E)enthalpy

2 Which of the following acids and its sodium salt are the best combination for buffering a solution at pH 4.30? (A)chloroacetic acid (Kₐ=1.35×10⁻³) (B)propanoic acid (Kₐ=1.3×10⁻⁵) (C)benzoic acid (Kₐ=6.4×10⁻⁵) (D)hypochlorous acid (Kₐ=3.5×10⁻⁸) (E)none of the above is acceptable