Class 10th Chemistry - Class 12 UP Board Chemistry

Chemical Reactions and Equations

Valency and Compound Formation Understanding valency is essential for writing chemical formulas and equations. Valency indicates the combining capacity of an element or ion, and compounds are formed by balancing the valencies of participating ions.

Valency Rules: - Elements with valency +1: e.g.,...

Which of the following are combination reactions?
(i) $2KCl{O}_3\&\#8594;2KCl+3O_2$
(ii) $MgO+H_{2}O\&\#8594;Mg(OH{)}_2$
(iii) $4Al+3O_2\&\#8594;2A{l}_2{O}_3$
(iv) $Zn+FeS{O}_4\&\#8594;ZnS{O}_4+Fe$

(ii) and (iii)

Which of the observations take place when a chemical change occurs?

<span class="fontstyle0">All of the above</span>

Which of the following are combination reactions?
(i) $2KCl{O}_3\&\#8594;2KCl+3O_2$
(ii) $MgO+H_{2}O\&\#8594;Mg(OH{)}_2$
(iii) $4Al+3O_2\&\#8594;2A{l}_2{O}_3$
(iv) $Zn+FeS{O}_4\&\#8594;ZnS{O}_4+Fe$

(ii) and (iii)

Which of the observations take place when a chemical change occurs?

<span class="fontstyle0">All of the above</span>

What is a chemical reaction?

A chemical reaction is a process where one chemical substance transforms into another new substance with entirely different chemical properties. It involves the breaking of old chemical bonds and the formation of new ones, leading to substances with distinct characteristics.

Define valency and explain its significance in chemistry.

Valency is the combining capacity of an element, indicating the number of electrons an atom will gain, lose, or share to form a chemical bond. Understanding valency is crucial for predicting how elements combine to form compounds, often demonstrated by the criss-cross method.