Answer:
Energy is added (postive enthalpy)
Explanation:
Ice melting means solid turns into liquid. Solid is more stable than liquid thus you must put in energy to weaken the forces of solid and turn it into liquid. Thus, you must put in energy to melt ice. This makes the enthalpy of the system to be positive.
Answer:
D. The electron-withdrawing fluorine atoms pull electron density from the oxygen in trifluoroacetate. The negative charge is more stabilized in trifluoroacetate by this effect.
Explanation:
The structures of trifluoroacetate and acetic acid are both shown in the image attached.
The trifluoroacetate anion (CF3CO2-), just like the acetate anion has in the middle, two oxygen atoms.
However, in the trifluoroacetate anion, there are also three electronegative fluorine atoms attached to the nearby carbon atom attached to the carbonyl, and these pull some electron density through the sigma bonding network away from the oxygen atoms, thereby spreading out the negative charge further. This effect, called the "inductive effect" stabilizes the anion formed,the trifouoroacetate anion is thus more stabilized than the acetate anion.
Hence, trifluoroacetic acid is a stronger acid than acetic acid, having a pKa of -0.18.
Heat= mass * change in temperature* specific heat
specific heat=409 J/kg K