Answer: 
Explanation: A double displacement reaction is one in which exchange of ions take place.
According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.

Matter? all matter is made of atoms and has mass and volume. i think hope it helps
Answer:
Physical Property
Explanation:
Density, mass, volume, color, melting and boiling points, etc. are all physical properties. No matter what changes, the chemical makeup stays the same.
Flamability, acidity, toxicity, etc. are chemical properties, because they chemically change the makeup of the object/thing.
Answer:Chemical reactions often involve changes in energy due to the breaking and formation of bonds. Reactions in which energy is released are exothermic reactions, while those that take in heat energy are endothermic. exothermicA description of a chemical reaction that releases heat energy to its surroundings.