Chemistry 12
Chemistry 12
Unit 2 Notes - Equilibrium
Chemistry 12 Tutorial 5 – The Equilibrium Constant (Keq)
What is Keq ?
The "K" in Keq stands for "Constant". The "eq" means that the reaction is at equilibrium.
Very roughly, Keq tells you the ratio of Products/Reactants for a given reaction at equilibrium at a certain temperature.
[Products] [Reactants]
K eq =
It's not quite this simple when we deal with real substances. Let's take an example. It has been found for the reaction: 2HI(g ) H2(g) + I2(g)
that if you take the [H2], the [I2] and the [HI] in an equilibrium mixture of these at 423 °C, the expression: [H 2 ] [I 2 ] = 0.0183 [HI] 2
The value of K eq The K eq expression
The value of this ratio stays at 0.0183 regardless of what we might try to do with the concentrations. The only thing that changes the value of Keq for a given reaction is the temperature!
Writing Keq Expressions
In the example just above this, the equation was: 2HI(g) and the Keq expression was:
Keq =
H2(g) + I2(g)
[H 2 ] [I 2 ] [HI] 2
Unit 2 Notes – Equilibrium
Page 1
Chemistry 12
Unit 2 Notes - Equilibrium
Notice a couple of things here. The concentrations of the products are on the top (numerator) and the concentration of the reactant is on the bottom. (denominator). Also, notice that the coefficient "2" in the "2HI" in the equation ends up as an exponent for [HI]
2 in the Keq expression. Thus we have [HI] in the denominator.
Notice that in the Equilibrium Constant Expression (Keq ), whatever is written on the right of the arrow in the equation (products) is on top and whatever is written on the left of the arrow in the equation (reactants) is on the bottom. This is always the case in a Keq expression, regardless of which reaction (forward or reverse) predominates at a certain time. *********************************************************
The Keq Expressions for Solids and Liquids
Consider the following reaction: CaCO3(s) CaO(s) + CO2(g)
Unit 2 Notes - Equilibrium
Chemistry 12 Tutorial 5 – The Equilibrium Constant (Keq)
What is Keq ?
The "K" in Keq stands for "Constant". The "eq" means that the reaction is at equilibrium.
Very roughly, Keq tells you the ratio of Products/Reactants for a given reaction at equilibrium at a certain temperature.
[Products] [Reactants]
K eq =
It's not quite this simple when we deal with real substances. Let's take an example. It has been found for the reaction: 2HI(g ) H2(g) + I2(g)
that if you take the [H2], the [I2] and the [HI] in an equilibrium mixture of these at 423 °C, the expression: [H 2 ] [I 2 ] = 0.0183 [HI] 2
The value of K eq The K eq expression
The value of this ratio stays at 0.0183 regardless of what we might try to do with the concentrations. The only thing that changes the value of Keq for a given reaction is the temperature!
Writing Keq Expressions
In the example just above this, the equation was: 2HI(g) and the Keq expression was:
Keq =
H2(g) + I2(g)
[H 2 ] [I 2 ] [HI] 2
Unit 2 Notes – Equilibrium
Page 1
Chemistry 12
Unit 2 Notes - Equilibrium
Notice a couple of things here. The concentrations of the products are on the top (numerator) and the concentration of the reactant is on the bottom. (denominator). Also, notice that the coefficient "2" in the "2HI" in the equation ends up as an exponent for [HI]
2 in the Keq expression. Thus we have [HI] in the denominator.
Notice that in the Equilibrium Constant Expression (Keq ), whatever is written on the right of the arrow in the equation (products) is on top and whatever is written on the left of the arrow in the equation (reactants) is on the bottom. This is always the case in a Keq expression, regardless of which reaction (forward or reverse) predominates at a certain time. *********************************************************
The Keq Expressions for Solids and Liquids
Consider the following reaction: CaCO3(s) CaO(s) + CO2(g)