CHEM- CH-1 - Chemical Reactions and Equations

NWERT CLASS 10

Chemical Reaction

whenever a chemical change occurs we say that a chemical reaction has taken place.

it involves the breaking and making of bonds between atoms to produce new substances.

observations that help determine whether a reacton has taken place

• change in state

• change in colour

• evolution of a gas

• change in temperature

word equation

it shows change of reactants to products through an arrow placed between them.

the reactants are written on the LHS with a + sign between them. similarly products are written on the RHS with a + sign btw them.

the arrow head points towards the products , shows the direction of the reactions.

skeletal equation

an equation which is not balanced as the mass is not the same on both sides of the equations.

Law of Conservation of mass

mass can neither be created nor destroyed in a chemical reaction.

What is aqueous?

when a reactant or the product is present as a solution in water.

what is written above or below the arrow in the equation?

reaction conditions such as:

• temperature

• catalyst

• pressure, etc…

Combination reactions

when 2 or more substances combine to form a single product

exothermic reactions

reactions in which heat is released along with the formation of products.

decomposition reaction

a single reactant breaks down to give simpler products

thermal decomposition

when a decomposition reaction occurs by heating

which reaction requires energy either in the form of heat, light, or electricity for breaking down the reactants

decomposition reactions

endothermic reaction

reactions in which energy is absorbed

precipitate

the insoluble substance formed in a reaction

precipitation reaction

any reaction that produces a precipitate

double displacement reactions

reactions in which there is an exchange of ions between the reaction

oxidation

if a substance gains oxygen or loses hydrogen during the reactions

reduction

if a substance loses oxygen or gains hydrogen.

redox reaction

a reaction in which one reactant gets oxidised while another gets reduced during a reaction

corrosion

when a metal is attacked by substances around it such as moisture,acids , etc

rancid

when fats and oils are oxidized they become rancid and their smell and taste change

how to avoid rancidity?

usually antioxidants are added to foods containing oil and fats,

manufacturers usually flush bags of chips with gas such as nitrogen to prevent oxidation