If you add 200 mL of water at 20 C to another 200mL of water at the same temperature what happpens to the kinetic energy and thermal energy of the combustion?

Answer 1

Until the very last words, your question doesn't say anything about any

combustion.

If you mean the combustion it took to warm the second beaker of water to

the temperature of 20° C, that energy is exactly reflected in the temperature

of the water. If the energy released by burning that alcohol or that gas, or

the electricity it took to heat that burner on the stove, had not been absorbed

by the water, then its temperature would not be 20° C.

Carrying a bottle of hot water around is a fine and effective way to move energy

from one place to another. Compared to other substances, water actually holds

an unusually great amount of it in a cupful.

Answer 2

When two substances of the same temperature are mixed, there is no change in the total kinetic energy or thermal energy of the system since they are simply redistributed between the two substances. The final temperature after mixing will be the same as the initial temperature, in this case, 20°C.