SHS

11
Activity Sheet
Quarter 2 – WEEK 2
Chemical Equilibrium

REGION VI – WESTERN VISAYAS

 Learning Activity Sheets (LAS) for General Chemistry 2

Name of Learner: ________________________________________________________

Grade and Section: _________ __________ Date: ________________

GENERAL CHEMISTRY 2 ACTIVITY SHEET NO. 3

Chemical Equilibrium

I. Learning Competency with Code

Explain chemical equilibrium in terms of the reaction rates of the forward and the
reverse reaction. (STEM_GC11CEIVb-e-145)

Calculate equilibrium constant and the pressure or concentration of reactants or

products in an equilibrium mixture. (STEM_GC11CEIVb-e-148)

II. Background Information for Learners

• A chemical reaction can achieve a state in which the forward and reverse
processes are occurring at the same rate. This condition is called chemical
equilibrium.
• In a reversible reaction, when the reactants start to form the products, the
products would then start to reform the reactants. The two opposing
processes happen at different rates but a certain point in the reaction will be
reached where the rates of the forward and backward reactions are the same –
chemical equilibrium.
• In a state of chemical equilibrium, since the rate of product formation is equal to
the rate of the reformation of the reactants, then the concentrations of the
reactants and products remain becomes constant.
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Figure 1. Changes in the rate of the forward and backward Figure 2. Changes in the amount of reactants and products in a
reactions in a reversible reaction. reversible reaction.

• The relationship between the concentrations of the reactants and products of the
system at equilibrium is described by the law of mass action. For an
equilibrium equation of the form,
aA + bB → cC + dD

the equilibrium – constant expression is written as

[𝐷]𝑑 [𝐶]𝑐 (𝑃𝐷 )𝑑 (𝑃𝐶 )𝑐
Kc = or Kp =
[𝐴]𝑎[𝐵]𝑏 (𝑃𝐴 )𝑎(𝑃𝐵 )𝑏

• Kc is expressed in terms of molar concentration while Kp is expressed in terms

of partial pressures.
 • For equilibrium reactions, pure solids and pure liquids are excluded in writing
equilibrium constant expressions.
• Examples:

• Equilibrium constant (Kc or Kp) provides an idea of the relative concentrations of

the reactants and products in an equilibrium mixture. Generally,

If K >> 1 (large K value), the equilibrium lies to the right and the products
predominate in the equilibrium mixture.

If K << 1 (small K value), the equilibrium lies to the left and the reactants
predominate in the equilibrium mixture.
If K ≈ 1, the reaction is at equilibrium; forward and reverse reactions are about
equally favorable

Sample Problem 1: Gaseous hydrogen iodide is placed in a closed container at 425

˚C, where it partially decomposes to hydrogen and iodine.

2 HI(g) H2(g) + I2(g)

At equilibrium it is found that [HI] = 3.53 x 10-3 M, [H2] = 4.79 x 10-4 M and [I2] = 4.79 x
10-4 M. What is the value of Kc at this temperature? Which is more dominant, reactant or
product?

[𝑯𝟐 ][𝑰𝟐 ]
Kc =
[𝑯𝑰]𝟐

Since K < 1, equilibrium lies to the left and the reactants predominate.

*Note: Kc and Kp are unitless.

Sample Problem 2: The reaction between H2 and N2 produces NH3. At equilibrium, it is

found that NH3 .= 98 atm, N2 = 45 atm and H2 = 55 atm. Determine Kp and indicate
whether the mixture is at equilibrium at 450 °C.
N2(g) + 3 H2(g) 2NH3(g)

(𝑵𝑯𝟑)𝟐 (𝟗𝟖)𝟐
Kp = = = = 1.28 x 10-3
(𝑵𝟐 )(𝑯𝟐 )𝟑 (𝟒𝟓)(𝟓𝟓)𝟑

Since K < 1, mixture is not at equilibrium; the reactants predominate.

III. Activity Proper

Activity 1. For the following reactions at equilibrium, write the equilibrium constant
expression and identify which between the reactants and products is dominant.
REACTION EQUILIBRIUM EQUILIBRIUM WHICH IS
CONSTANT CONSTANT MORE
VALUE EXPRESSION DOMINANT?
1. 2 NOBr(g) 2 NO(g) + Br2(g) Kc = 1.5 x 10-10

2. Br2(g) + Cl2(g) 2 BrCl(g) Kp = 2.5 x 109

3. 2 SO2(g) + O2(g) 2 SO3(g) Kp = 5.0 x 1012

4. PbCl2(s) Pb2+(aq) + 2 Cl-(aq) Kc = 5.8 x 10-18

5. CaCO3(s) CaO(s) + CO2(g) Kc = 2.4 x 10-7

Activity 2. Problem Solving

1. An aqueous solution of acetic acid is found to have the following equilibrium

concentrations at 298 K: [CH3COOH] = 1.65 x 10-2 M; [H+] = 5.44 x 10-4 M; and
[CH3COO-] = 5.44 x 10 -4 M. Calculate the equilibrium constant, Kc and determine
whether the reactant or product is dominant.

CH3COOH (aq) H+ (aq) + CH3COO- (aq)

IV. Reflection

Give one important application of chemical equilibrium. Briefly describe in 3-5 sentences
the significance of chemical equilibrium in your chosen application.

V. References:

Brown T.L. et al. (2014). Chemistry: The Central Science (13th ed.). New York City, New
York: Pearson Learning Solutions.

Commission on Higher Education. (2016). Teaching Guide for Senior High School:
General Chemistry 2. Quezon City, Philippines: EC-TEC Commercial.
 Learning Activity Sheets (LAS) for General Chemistry 2

Name of Learner: ________________________________________________________

Grade and Section: _________ __________ Date: ________________

GENERAL CHEMISTRY 2 ACTIVITY SHEET NO. 4

Chemical Equilibrium

I. Learning Competency with Code

State the Le Chatelier’s principle and apply it qualitatively to describe the effect of
changes in pressure, concentration and temperature on a system at equilibrium.
(STEM_GC11CE-IVb-e-149)

II. Background Information for Learners

• Le Chatelier’s Principle states that if a system at equilibrium is disturbed by a

change in concentration, pressure or temperature, the system will shift its
equilibrium position so as to counter the effect of the disturbance.

• Concentration: adding or removing a reactant or products

If a substance is added to a system at equilibrium, the system reacts to

consume some of the substance. If a substance is removed from a system, the
system reacts to produce more of the substance.

• Pressure: changing the pressure by changing the volume

At constant temperature, reducing the volume (increasing pressure) of a

gaseous equilibrium mixture causes the system to shift in the direction that
has less number of moles of gas. On the other hand, increasing the volume
(decreasing pressure) of the equilibrium mixture causes the system to shift in
the direction that has greater number of moles of gas.

• Temperature:

If the temperature of a system at equilibrium is increased, the system reacts as if

we added a reactant to an endothermic reaction or a product to an
exothermic reaction. The equilibrium shifts in the direction that consumes the
“excess reactant,” namely heat.
 • Consider the reaction below with ΔH = + 28.5 kJ,

Stress Applied Equilibrium Shift Effect

1. Adding N2 or shift to the right (product side) Increase concentration of the product;
H2 decrease concentration of both reactants.
2. Adding NH3 shift to the left (reactant side) Increase concentration of the reactants;
decrease concentration of the product.
3. Increasing shift to the right; product side Increase concentration of the product;
Pressure has less number of moles of decrease concentration of both reactants.
(reduced gas (2 moles) than the reactant
volume) side(4 moles)
4. Decreasing shift to the left; reactant side Increase concentration of the reactants;
Pressure has greater number of moles of decrease concentration of the product.
(increased gas (4 moles) than the product
volume) side (2 moles)
5. Increasing shift to the right; reaction is Increase concentration of the product;
temperature endothermic decrease concentration of both reactants
6. Decreasing shift to the left; reaction is Increase concentration of the reactants;
temperature endothermic decrease concentration of the product

III. Activity Proper

Direction: Complete the table below by writing left (reactant side), right (product
side) or none for the equilibrium shift and increases, decreases or remains the same
for the concentrations of reactants and products.

CH4(g) + 2H2S(g) CS2(s) + 4H2(g) ΔH = +127.0 kJ

STRESS EQUILIBRIUM [CH4] [H2S] [CS2] [H2]

SHIFT
1. Add CH4 right ----- decreases Increases increases
2. Add H2S -----
3. Add H2 -----
4. Remove CH4 -----
5. Remove CS2 -----
6. Increase
Temperature
7. Decrease
Temperature
8. Increase
Pressure
9. Decrease
Pressure
10. Add H2O

IV. Reflection

VI. References:

Brown T.L. et al. (2014). Chemistry: The Central Science (13th ed.). New York City, New
York: Pearson Learning Solutions.

Commission on Higher Education. (2016). Teaching Guide for Senior High School:
General Chemistry 2. Quezon City, Philippines: EC-TEC Commercial.