g For each of the following cases, indicate whether the first entity is greater than, less than or equal to the second entity. W
rite 'G' for greater, 'L' for less and 'E' for equal (The letters must be in uppercase) Enthalpy of combustion of a fuel at STP Enthalpy of combustion of the same fuel at 20°C Enthalpy of formation of methane at STP Enthalpy of formation of methane at 1000 K and 100 kPa Enthalpy of combustion of gas propane with stoichiometric air Enthalpy of combustion of gas propane with 150% theoretical air. Adiabatic Flame Temperature of combustion reaction of liquid butane with equivalence ratio of 1.5 Adiabatic Flame Temperature
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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.
