STPM Chemistry Form 6 Notes – Terminology and Concepts: Chemical Equilibrium (Part 2)

by BerryBerryTeacher

in Berry Reference (Notes)

This is Part 2 of STPM Chemistry notes on Chemical Equilibrium for Form 6 students brought to you by Berry Berry Easy. So for those who missed out on Part 1 of the notes, it was on reversible reaction, dynamic equilibrium, the equilibrium law and constants. The Berry Berry Teacher hopes that all Berry Readers have grasp the concept of chemical equilibrium where there is no net change over time in activities and concentration of products and reactants.

In this set of notes, the focus is on the equilibrium types. Make sure you can understand the differences between the homogeneous and heterogenous equilibriums. Learn also the way to classify/use the equilibrium constants according to situations. Let us move on to the notes.

STPM Form 6 – Terminology and Concepts: Chemical Equilibrium (Part 2)

1. Equilibrium Constant (in terms of partial pressure), Kp

  • Kp can only be applied to gas reactions.
  • Kc and Kp are not numerically equal.
  • The total number of moles (in a gas reaction) is the same.
    Example: aA(g) + bB(g) <—->  cC(g) + dD(g)
  • The equilibrium constant (in term of partial pressure), Kp
    Kp = (PC)c (PD)d / (PA)a (PB)b
  • The equilibrium constant (in term of concentration), Kc
    Kc = [C]c[D]d / [A]a[B]b
  • Kp = Kc
    Example: 2HI(g) <–> H2(g) + I2(g)
  • The equilibrium constant (in term of partial pressure), Kp
    Kp = (PH2) (PI2) / (PHI)2

2. Homogeneous Equilibrium

  • All substances are in the same physical states (all gases or all liquids).
    Example: N2(g) + 3H2(g) <–> 2NH3(g)
    Kp = (PNH3)2 / (PN2) (PH2)3

3. Heterogeneous Equilibrium

  • The substances are in different physical states (a mixture of solids, liquids or gases)
    Example: CaCO3(s) <–> CaO(s) + CO2(g)
    Kp = PCO2

    * The concentrations of solids and pure liquids are constants. In the expressions for Kc and Kp, solids and pure liquids are left out.

Don’t forget to come back to Berry Berry Easy for part 3 of this Chemical Equilibrium chapter. It’ll contain the gist of this chapter.

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February 8, 2011
February 9, 2011

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