Chemistry !
(20 points)

questions are in the

(sorry about the quality)

Explanation:

1) write a balanced double replacement chemical equation?

Double replacement:

It is the reaction in which two compound exchange their ions and form new compounds.

AB + CD → AC +BD

For example:

Na₂S + 2HCl → 2NaCl + H₂S

Double replacement reaction is also called metathesis. It is the reaction in which the two compound react with each other their cation and anions are exchange and form two new products or compound.

In given reaction sodium sulfide react with hydrochloric acid and form hydrogen sulfide and sodium chloride. The cation of sodium sulfide exchange with cation of hydrochloric acid and form new product.

2) For above equation demonstrate it obey law of conservation of mass. calculate the mass of reactant and product.

Law of conservation of mass:

According to the law of conservation mass, mass can neither be created nor destroyed in a chemical equation.

Explanation:

This law was given by french chemist  Antoine Lavoisier in 1789. According to this law mass of reactant and mass of product must be equal, because masses are not created or destroyed in a chemical reaction.

For example:

Na₂S    +          2HCl      →     2NaCl     +      H₂S

(23×2 g + 32 g )    36.5×2           2 (23+35.5)g  2+32 g

78 g + 73 g                                     117 g + 34 g

151 g                                                     151 g

we can see the mass of reactants are equal to mass of product. Thus this reaction completely hold the law of conservation of mass.

3) Which two quantities are always conserved in chemical reaction?

Mass and energy are always conserved in the reaction.

Law of conservation of mass:

According to the law of conservation mass, mass can neither be created nor destroyed in a chemical equation.

Explanation:

This law was given by french chemist  Antoine Lavoisier in 1789. According to this law mass of reactant and mass of product must be equal, because masses are not created or destroyed in a chemical reaction.

For example:

In given photosynthesis reaction:

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂  

there are six carbon atoms, eighteen oxygen atoms and twelve hydrogen atoms on the both side of equation so this reaction followed the law of conservation of mass