To show how substances in a chemical reaction interact and to keep track of all elements and the number of atoms in each element on each side of the equation.The purpose of writing a balanced chemical equation is to know: the reactants (starting material) and products (end results) that occur. the ratios in which they react so you can calculate how much reactants you need and how much products can be formed.
boiling, salt water will separate the salt from the water through the physical change of water from a liquid to a gas, leaving you with just salt left over.
solar thermal energy can be even used to produce air conditioning I'm not understanding your question due to the fact that solar thermal energy produces hot water provides heat for houses and warms buildings great for space heating and can provide electricity
