Question

class 10 notes of 1 chapter science​

Answer 1

Introduction to Chemical Reactions and Equations

Physical and chemical changes

Chemical change – one or more new substances with new physical and chemical properties are formed.

Chemical Reactions and Equations-1

Here, when copper sulphate reacts with iron, two new substances, i.e., ferrous sulphate and copper are formed.

Chemical-Reactions-and-Equations-2

Physical change – change in colour or state occurs but no new substance is formed.

Example: Water changes to steam on boiling but no new substance is formed(Even though steam and water look different when they are made to react with a piece of Na, they react the same way and give the exact same products). This involves only a change in state (liquid to vapour).

Observations that help determine a chemical reaction

A chemical reaction can be determined with the help of any of the following observations:

a) Evolution of a gas

b) Change in temperature

c) Formation of a precipitate

d) Change in colour

e) Change of state

Chemical reaction

Chemical reactions are chemical changes in which reactants transform into products by making or breaking of bonds(or both) between different atoms.

Types of chemical reactions

Taking into consideration different factors, chemical reactions are grouped into multiple categories.

Few examples are:

● Combination

● Decomposition

● Single Displacement

● Double displacement

● Redox

● Endothermic

● Exothermic

● Precipitation

● Neutralisation

Chemical Reactions and Equations I

Word equation

A word equation is a chemical reaction expressed in words rather than chemical formulas. It helps identify the reactants and products in a chemical reaction.

For example,

Sodium + Chlorine → Sodium chloride

The above equation means: “Sodium reacts with chlorine to form sodium chloride.”

Symbols of elements and their valencies

A symbol is the chemical code for an element. Each element has one or two-letter atomic symbol, which is the abbreviated form of its name.

Valency is the combining capacity of an element. It can be considered as the number of electrons lost, gain or shared by an atom when it combines with another atom to form a molecule.

Answer 2

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