There are two stable isotopes of bromine . Their masses are 78.9183 u and 80.9163 u. If the average atomic mass of bromine is 79.90 u, what is the natural abundance of the lighter isotope

A5 mole sample of liquid acetone is converted to a gas at 75.0°c. if 628 j are required to raise the temperature of the liquid to the boiling point, 15.600 kj are required to evaporate the liquid, and 712 j are required to raise the final temperature to 75.0°c, what is the total energy required for the conversion?