Chemical Substances, Reactions and Essential Resources(WJEC)

Chemical Reaction

A process where reactants transform into products through the breaking and forming of chemical bonds.

Evidence of a Chemical Reaction:

Bubbling or odor change or change in pH or changes in electrical conductivity

Precipitate

A solid formed from a solution.

Types of Energy Change

Exothermic (releases heat) or Endothermic (absorbs heat).

Photo Reaction

Energy release as light.

Combination/Synthesis Reaction

Simple substances combine to form a complex substance.

Decomopisiton reaction

A compound breaks down into simpler substances.

Displacement

One element replaces another in a compound.

Electrons

Parts of two ionic compounds exchange.

Combustion

Substance reacts with oxygen, releasing energy.

Factors effecting rate of reaction

Concentration, Temperature, Surface Area, Catalysts, Inhibitors.

Activation Energy

Minimum energy for reactants to form products.

Catalyst

Lowers activation energy, increasing reaction rate.

Energy in Chemical Reactions

Enthalpy

EXOthermic

Release energy (heat).

ENDOthermic

Absorb energy (heat).

Spontaneity

Measure of disorder.

Dynamic Equilibrium

Rates of forward and reverse reactions are equal.

Le Chatlier’s Principle

System adjusts to minimize disturbances.

Chromatography

Separating components based on movement through phases.