101

 

What are derived units?

Derived units are units which may be expressed in terms of base units, by means of mathematical symbols of multiplication and division.

E.g. velocity, pressure, energy, power etc.

102

What is a chemical reaction?

Chemical reaction is a process that leads to the transformation of one set of chemical substances to another.

103

What are chemical equations?

A chemical equation is the symbolic representation of a chemical reaction, wherein the reactant entities are given on the left-hand side and the product entities on the right-hand side.

The coefficients next to the symbols and formulae of entities, are the absolute values of the stoichiometric numbers.

104

What is a physical change?

Physical changes are changes, affecting the form of a chemical substance, but not its chemical composition.

105

What is a chemical change?

Chemical changes occur when a substance combines with another to form a new substance, or alternatively, decomposes into two or more different substances.

When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products are generated.

An example of a chemical change is the reaction between sodium and water to produce sodium hydroxide and hydrogen.

106

What is Thermal equilibrium?

Two physical systems are in thermal equilibrium if no heat flows between them when they are connected by a path permeable to heat.

Thermal equilibrium obeys the Zeroth Law of Thermodynamics.

107

 

What is Osmosis?

 

When two liquids with different concentrations of a solute are separated by a semipermeable membrane, the fluid has a tendency to move from low to high solute concentrations for chemical potential equilibrium.

 

This natural movement of the fluid from low to high solute concentrations, for attaining a chemical potential equilibrium is called Osmosis.

108

 

What is reverse osmosis?

 

Reverse osmosis (RO) is a water purification technology that uses a semipermeable membrane, to remove larger particles from drinking water.

 

In reverse osmosis, an applied pressure is used to overcome osmotic pressure.

 

Reverse osmosis can remove many types of molecules and ions from solutions, including bacteria, and is used in both industrial processes and the production of potable water.

 

The solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side.

 

To be "selective", this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely.

 

109

 

What is a solution?

 

A solution is a homogeneous mixture composed of only one phase.

 

In such a mixture, a solute is a substance dissolved in another substance, known as a solvent.

 

The solution more or less takes on the characteristics of the solvent including its phase, and the solvent is commonly the major fraction of the mixture.

 

The concentration of a solute in a solution is a measure of how much of that solute is dissolved in the solvent, with regard to how much solvent is present.

 

110

 

What is a mixture?

A mixture is a material system made up of two or more different substances, which are mixed but are not combined chemically.

A mixture refers to the physical combination of two or more substances, on which the identities are retained and are mixed in the form of solutions, suspensions, and colloids.