Exothermic change and endothermic change
Endothermic change - A process or chemical reaction in which heat energy is produced and released to the surroundings. ΔH for an exothermic change has a negative value.
Exothermic change - A process or chemical reaction that takes in heat from the surroundings. ΔH for an endothermic change has a positive value.
Mixture of substance and diffusion
The chemical world is very complex, owing to the vast range of pure substances available and to the variety of ways in which these pure substances can mix with each other.
Each mixture must be made from at least two parts, which may be either solid, liquid or gas. There are a number of different ways in which the three states can be combined.
In some, the states are completely mixed to become one single state or phase. Technically, the term solution is used for this type of mixture composed of two or more substances.
Solid salt dissolves in liquid water to produce a liquid mixture. This is called a salt solution
The solid has completely disappeared into the liquid. In general terms, the solid that dissolves in the liquid is called the solute.
The liquid in which the solid dissolves is called the solvent.
In other types of mixture, the states remain separate. One phase is broken up into small particles, droplets or bubbles, within the main phase.
The most obvious example of this type of mixture is a ( suspension - a mixture containing small particles of an insoluble solid, or droplets of an insoluble liquid, spread (suspended) throughout a liquid ) of fine particles of a solid in a liquid, such as we often get after a precipitation reaction.
Precipitation reaction defines the process in which salt is created with 2 soluble salt