physical chemistry definitions

first ionisation energy

the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous positive ions

relative atomic mass

Relative atomic mass,Ar,is the average mass of an atom of an element compared with 112th of the mass of an atom of carbon - 12

Relative molecular mass 

The relative molecular mass,Mr,of a molecule is the mass of that molecule compared with 1/12th the mass of an atom of carbon - 12

relative formula mass

The relative formula mass,Mr of a formula unit is the average mass of one formula unit compared with 1/12th of the mass of an atom of carbon - 12  

A mole 

The amount of any substance which contains the same number of particles (atoms,ions or molecules) as there are carbon atoms in exactly 12g of the carbon - 12 isotope

Avogadro's law 

Equal volumes of gases at the same temperature and same pressure contain equal numbers of molecules (particles)

Molar volume 

1 mole of any gas at room temperature and pressure (rtp) occupies a volume of 24dm3.

Molecular formula or formula unit 

Is the actual number of atoms of each element that are present in a molecule or formula unit 

Empirical formula 

The simplest whole number ratio of atoms of each element that are present in a compound 

Law of conservation of mass 

No atoms are lost or made in a chemical reaction; they are only rearranged. The total mass of the products is equal to the total mass of the reactants. 

Percentage yield 

Shows how much product was actually made compared with the amount of product that was expected as a percentage 

Theoretical yield 

The maximum mass of product expected for the reaction,calculated using reacting masses 

Actual yield 

The mass of product that is actually obtained from the real chemical reaction 

Equilibrium

Dynamic equilibrium is reached when the forward and reverse reactions occur at exactly the same rate in a closed system 

Dynamic equilibrium 

The equilibrium that exists in a closed system where the rate of the forward reaction is equal to the rate of backwards reaction 

Homogeneous 

Is an equilibrium in which all the reactants are in the same phase 

Heterogeneous

Is an equilibrium in which the reactants and products are in a different phase 

Le chatelier's principle 

• If a dynamic equilibrium is disturbed by changing the conditions,the position of the equilibrium shifts the counteract the change to reestablish equilibrium

Kc

• If Kc is close to 1,then the concentrations of products and reactants are similar and positions equilibrium lies near the centre