Easy summary for chemical equilibrium a level chemistry

Easy summary for chemical equilibrium a level chemistry

Learning outcomes 

You should be able to: ■

■ explain what is meant by a reversible reaction and dynamic equilibrium ■

■ state Le Chatelier’s principle and apply it to deduce qualitatively the eff ect of changes in temperature, concentration or pressure on a system at equilibrium ■

■ state whether changes in temperature, concentration or pressure or the presence of a catalyst aff ect the value of the equilibrium constant for a reaction ■

■ deduce expressions for equilibrium constants in terms of concentrations, Kc , and partial pressure, Kp 

■ calculate: – the value of equilibrium constants in terms of concentrations or partial pressures – the quantities of substances present at equilibrium ■

■ describe and explain the conditions used in the Haber process and the Contact process ■

■ show understanding of, and use, the Brønsted– Lowry theory of acids and bases ■

■ explain qualitatively the diff erences in behaviour between strong and weak acids and bases and the pH values of their aqueous solutions in terms of the extent of dissociation.

Summary 

■ A reversible reaction is one in which the products can be changed back to reactants. 

■ Chemical equilibrium is dynamic because the backward and forward reactions are both occurring at the same time. 

■ A chemical equilibrium is reached when the rates of the forward and reverse reactions are equal. 

■ Le Chatelier’s principle states that when the conditions in a chemical equilibrium change, the position of equilibrium shifts to oppose the change. 

■ Changes in temperature, pressure and concentration of reactants and products affect the position of equilibrium. 

■ For an equilibrium reaction, there is a relationship between the concentrations of the reactants and products which is given by the equilibrium constant K. 

■ Equilibrium constants in terms of concentrations, Kc , and partial pressure, Kp, can be deduced from appropriate data.

■ The quantities of reactants and products present at equilibrium can be calculated from the equilibrium expression and a value of Kc (or Kp), given appropriate data. 

■ A change in temperature affects the value of the equilibrium constant for a reaction but changes in concentration, pressure or the presence of a catalyst do not affect the value of the equilibrium constant. 

■ The conditions used in the Haber process and the Contact process are chosen so that a good yield of product is made. 

■ The Brønsted–Lowry theory of acids and bases states that acids are proton donors and bases are proton acceptors. 

■ Strong acids and bases are completely ionised in aqueous solution whereas weak acids and bases are only slightly ionised. 

■ Strong and weak acids and bases can be distinguished by the pH values of their aqueous solutions.