Science 10 (Chemistry): 6 - Chemical Reactions & The Mole

Chemical Reactions

when one or more substances change to form different substances evident through the changes in matter and energy.

reactants and products

reactants are used, properties disappear → products are formed, properties appear

5 Evidences of Chemical Change

energy change in soroundings, formation of gas, formation of precipirtate, change in color and odor.

Process of Chemical Reactions

a reaction occurs when reactant molecules collide with each other and energy is absorved to break atom bonds and these atoms are rearranged and form new bonds to make new products

1st Step of CR

collision of reactant molecules

2nd Step of CR

absorption of energy to break atomic bonds

3rd Step of CR

rearrangement of atoms to form new bonds

4th Step of CR

release of energy to form new bonds.

5th Step of CR

the energy changes

2 Types of Energy Changes

endothermic and exothermic reactions

Endothermic Reaction

temperature decreases and reactants absorb energy to produce products and breaks down chemical bond(thermal energy is a reactant)

Exothermic Reaction

temperature increases, reactants release energy to produce products and form new bonds (thermal energy is a product)

Endothermic Example

thermal e. + 6H₂O + 6CO₂ → C₆H₁₂O₆ +6O₂
photosynthesis

Exothermic Examples

C₆H₁₂O₆ + 6O₂ → thermal e. 6H₂O + 6CO₂

Energy Change in Sorroundings

temperature has decreases or increases, change in light ot sound

Formation of Precipitate

ionic product has low solubility, solid particles appear as clear / opaque in a solution

Change in Color

color disappears or appears, color lightens or new color appears.

Odor Change

odor disappears or appears.

Law of Conservation of Energy

states that energy cannot be created or destroyed only transferred.

Double Replacement

cations and anions exchange partners to form new compounds

Combustion

adding oxygen to form most common oxide, reactions are exothermic

Single Replacement

one element replaces another in a compound

Formation

two or more reactants combine to make a new compounds or elements

Avagardo’s Number

6.02 × 10²³

Amadeo Avagadro

studied quantitive hypotheses about gases which led to the mole concept