Term: 2^{nd} Term
Week: 7
Class: Senior Secondary School 1
Age: 15 years
Duration: 40 minutes of 5 periods each
Date:
Subject: Chemistry
Topic: Gas laws II
SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to
INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source
INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures
INSTRUCTIONAL PROCEDURES
PERIOD 12
PRESENTATION 
TEACHER’S ACTIVITY 
STUDENT’S ACTIVITY 
STEP 1 INTRODUCTION 
The teacher reviews the previous lesson on Boyle’s aw, Charles’ law and the general gas laws 
Students pay attention 
STEP 2 EXPLANATION 
He states and explains GayLussac and Avogadro’s law, stating their formulae repetitively.

Students pay attention and participates 
STEP 3 DEMONSTRATION 
He outlines the ideal gas equations and solves problems on all the gas laws learnt 
Students pay attention and participate 
STEP 4 NOTE TAKING 
The teacher writes a summarized note on the board 
The students copy the note in their books 
NOTE
GAS LAWS
GAY LUSSAC’S LAW OF COMBINING VOLUME.
GayLussac’s law is a gas law which states that the pressure exerted by a gas (of a given mass and kept at a constant volume) varies directly with the absolute temperature of the gas. In other words, the pressure exerted by a gas is proportional to the temperature of the gas when the mass is fixed and the volume is constant.
This law was formulated by the French chemist Joseph GayLussac in the year 1808. The mathematical expression of GayLussac’s law can be written as follows:
P ∝ T ; P/T = k
Where:
The relationship between the pressure and absolute temperature of a given mass of gas (at constant volume) can be illustrated graphically as follows.
Formula and Derivation
GayLussac’s law implies that the ratio of the initial pressure and temperature is equal to the ratio of the final pressure and temperature for a gas of a fixed mass kept at a constant volume. This formula can be expressed as follows:
(P_{1}/T_{1}) = (P_{2}/T_{2})
Where:
This expression can be derived from the pressuretemperature proportionality for gas. Since P ∝ T for gases of fixed mass kept at constant volume:
P_{1}/T_{1} = k (initial pressure/ initial temperature = constant)
P_{2}/T_{2} = k (final pressure/ final temperature = constant)
Therefore, P_{1}/T_{1} = P_{2}/T_{2} = k
Or, P_{1}T_{2} = P_{2}T_{1}
Solved Exercises on GayLussac’s Law
Exercise 1
The pressure of a gas in a cylinder when it is heated to a temperature of 250K is 1.5 atm. What was the initial temperature of the gas if its initial pressure was 1 atm?
Solution
Given,
Initial pressure, P_{1} = 1 atm
Final pressure, P_{2} = 1.5 atm
Final temperature, T_{2} = 250 K
As per GayLussac’s Law, P_{1}T_{2} = P_{2}T_{1}
Therefore, T_{1} = (P_{1}T_{2})/P_{2} = (1*250)/(1.5) = 166.66 Kelvin.
Exercise 2
At a temperature of 300 K, the pressure of the gas in a deodorant can is 3 atm. Calculate the pressure of the gas when it is heated to 900 K.
Solution
Initial pressure, P_{1} = 3 atm
Initial temperature, T_{1} = 300K
Final temperature, T_{2} = 900 K
Therefore, final pressure (P_{2}) = (P_{1}T_{2})/T_{1} = (3 atm*900K)/300K = 9 atm.
Avogadro’s Law
It states that equal volume of all gases at the same temperature and pressure contain the same number of molecules irrespective of their physical and chemical properties
IDEAL GAS EQUATIONS
The ideal gas law is derived from the observational work of Robert Boyle, GayLussac and Amedeo Avogadro. Combining their observations into a single expression, we arrive at the Ideal gas equation, which describes all the relationships simultaneously.
The three individual expressions are as follows:
Boyle’s Law
V∝1/P
Charles’s Law
V∝T
Avagadro’s Law
V∝n
Combining these three expressions, we get
V∝nT/P
The above equation shows that volume is proportional to the number of moles and the temperature while inversely proportional to the pressure.
This expression can be rewritten as follows:
V=RnT=nRT
P P
Multiplying both sides of the equation by P to clear off the fraction, we get
PV=nRT
The above equation is known as the ideal gas equation.
Ideal Gas Solved Problems
V=nRT/P
Substituting the values as follows, we get
V=[(2.34g/44g.mol^{−}^{1})(0.08206L atm mol^{−}^{1} K^{−}^{1}) (273.0K)]/1.00atm
V=1.19L
Solution:
To determine the temperature, rearrange the ideal gas equation as follows:
T=PV/nR
Substituting the value, we get
T=(1.95atm))(12.30L)/(0.654mol)(0.08206L atm mol^{−}^{1 }K^{−}^{1})
T=447K
EVALUATION: 1. State GayLussac’s law
I) How many moles of gas are in the tire?
II) Assuming air is 80% nitrogen and 20% oxygen, what mass of air is in the tire?
5. A 2.50L volume of hydrogen measured at –196 °C is warmed to 100 °C. Calculate the volume of the gas at the higher temperature, assuming no change in pressure.
6. A weather balloon contains 8.80 moles of helium at a pressure of 0.992 atm and a temperature of 25 °C at ground level. What is the volume of the balloon under these conditions?
CLASSWORK: As in evaluation
CONCLUSION: The teacher commends the students positively