Summary (CAIE) Cambridge A Level Chemistry (9701)- Chemical Equilibria

Cambridge International AS and A Level Chemistry (9701)
University of Indonesia CHEM 004
Summary & 15’s Chemical Equilibria Practice Exam Solutions




Chemical Equilibria

, Equilibrium Concept

IRREVERSIBLE REACTION REVERSIBLE REACTION

 An irreversible reaction is a reaction  A reversible reaction is a reaction
that takes place in the same that goes in both directions (back
direction or a reaction that cannot and forth). In this case the product
reversed. can react again to form reactants.

 CH4(g) + 2 O2(g) CO2(g) + 2 H2O(g)  N2(g) + 3 H2(g)  2 NH3(g)

 The reaction to the right is called
the forward reaction, the reaction
to the left is called the reverse
reaction
Equilibrium State
Concentration (M) Characteristic of equilibrium


 Equilibrium time is obtained
when the rate of the forward
reaction = the rate of the
reverse reaction
 Although in a state of
equilibrium the
concentrations of the
reactants and products
remain constant,
 The reaction continues at the
molecular level, so this
equilibrium is called a
Equilibrium Time
Dynamic Equilibrium.
 It requires a closed system

, Equilibrium Type

HOMOGENEOUS EQUILIBRIUM HETEROGENEOUS EQUILIBRIUM

 Homogeneous Equilibrium:  Heterogeneous Equilibrium:
Equilibrium in which all the Equilibrium consisting of two or
components are in one phase. more phases.

 N2(g) + 3 H2(g)  2 NH3(g)  CaCO3(s)  CaO(s) + CO2(g)


 CH3COOH(aq)  CH3COO-(aq) + H+(aq)  Ag2CrO4(s)  2 Ag+(aq) + CrO42-(aq)




Laws and Provisions of Equilibrium
The product of the equilibrium concentrations of a substance on the right
side divided by the product of the equilibrium concentrations of a substance
on the left side, each raised to the power of its reaction coefficient, has a
certain value at a certain temperature.

aA + bB  cC + dD

Concentration Equilibrium Pressure Equilibrium Constant
Constant (Kc) (Kp)




 Aqueous (aq) and gas (g)  gas (g)
 Solid (s) and liquid (l)  solid (s), liquid (l), aqueous
(aq)
Kp = Kc (RT)n The partial pressure of each gas is
proportional to the moles in the
R = ideal gas constant balanced state.
T = absolute temperature The total pressure of the gases is
the sum of the partial pressures
n = the number of product of all the gases
coefficients minus the number
of reactant coefficients