To calculate conservation of mechanical energy, initial mechanical energy is subtracted from final mechanical energy true or false?

True according to a quick google search.

Yes, if it does not change, then the mechanical energy could be conserved.

However, there is a catch, that catch is that the total mechanical energy could have fluctuated in between. A quantity is conserved if it does not change. The only, definite way to calculate conservation of mechanical energy is to show that its time derivative is 0.

With that being said, the total mechanical energy of a system could have been conserved if the difference between the initial and the final mechanical energy is the 0, but it is not certain.

Think of it like a parabola, if the final and initial mechanical energy are the same, there still can be great variation in between.

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)