Second Term Lesson Note for Week Seven
Class : SSS 2
Subject : Physics
Topic : The Gas laws
Duration : 40 Minutes
Period : Single Period
Reference Book :
New School Physics for Senior Secondary School, SSS 1 – 3.
Lagos State Unified schemes of work for Senior Secondary Schools SSS 1 – 3.
Online Resources
Instructional Material : Chart showing the relationships in gas laws; Boyle’s law, Charles’ law and general gas law Equations.
Learning Objectives : By the end of the lesson learners will be able to :
i. Discuss the behavior of gases.
ii. State and explain the Boyle’s law, Charles’ law
iii. Explains the Pressure law and General gas law
Content :
GAS LAWS
In an attempt to study the behavior of gases in relation to volume, temperature and pressure, the following conditions are investigated :
- variation of volume with pressure at constant temperature, Boyle’s law
- variation of volume with temperature at constant pressure, Charles’ law
- variation of pressure with temperature at constant volume, pressure law
Boyle’s Law
Boyle’s law states that the pressure of a fixed mass of gas varies inversely as the volume at constant temperature.
P ∝ 1/V …………. Equation 1
P = k/ V …………. Equation 2
K = PV ……………. Equation 3
Where k = constant, Hence :
P1 V1 = P2 V2 …………….. Equation 4
Charles’ Law
Charles law states that for a fixed mass of gas at constant pressure, the volume is proportional to its absolute temperature
V ∝ T ………….. Equation 5
V = K T …………… Equation 6
K = V / T ……………. Equation 7
Where K = constant, Hence :
V1/ T1 = V2 / T2 ………… Equation 8
Pressure Law
Pressure law states that the pressure of a fixed mass of gas at constant volume is proportional to its absolute temperature.
—8
—9
Absolute Zero of Temperature
When the graphs of volume – temperature or pressure – temperature are extrapolated backwards they cut the temperature axis at -273°C. This temperature is called absolute zero, the temperature at which the volume of the gas theoretically becomes zero as it is being cooled. At this temperature, molecules of gas stop moving completely. This temperature is a mere assumption, as gases are known to liquefy more often than not before such a temperature is reached.
General gas Law
The general gas law is the combination of the Boyle’s, Charles and Pressure Law.
It follows That :
From Boyle’s law
From Charles’ law
From Gay-Lussac’s or Pressure law
In combination, we have
—11
—12
Equation 12 is known as general gas law or relation. This can be written in the form:
—13
Where: n=number of moles of gas
R=the universal molar gas constant = 8.31JK-1
CLASSWORK 7
State these laws and write its mathematical expression
Charles’ law
Boyle’s law
A vessel is filled with a gas at a temperature 500C and a pressure of 76cmHg. Calculate the final pressure if the volume of the gas is doubled while it is heated to 900C
ASSIGNMENT 7
SECTION A
The equation PxVyTz = constant is Boyle’s law if (a) x=0, y=0, z=1 (b) x=1, y=0, z=0 (c) x=1, y=1, z=0 (d) x=1, y=1, z=1 (e) x=1, y=1, z=-1
A column of air 10cm long is trapped in a tube at 270C. What is the length of the volume at 1000C? (a) 12.4cm (b) 13.7cm (c) 18.5cm (d) 37.0cm (e) 100cm
The volume of certain quantity of gas at 270C is 1200cm3. Calculate its volume at 1270C if the pressure remains constant. (a) 300cm3 (b) 400cm3 (c) 1000cm3 (d) 1600cm3 (e) 250cm3
A fixed mass of gas of volume 600cm3 at a temperature of 270C is cooled at constant pressure to a temperature of 00C. What is the change in volume? (a) 54cm3 (b) 273cm3 (c) 300cm3 (d) 546cm3 (e) 600cm3
A mass of gas occupies 20cm3 at 50C and 760mmHg pressure. What is its volume at 300C and 800mmHg pressure? (a) 41.4cm3 (b) 20.7cm3 (c) 50cm3 (d) 0.4cm3 (e) 25cm3
SECTION B
(a) State the ideal gas equation (b) Draw graphs to show Boyle’s law and Charles law
(a) What is meant by absolute zero of temperature? (b) State the assumptions of the kinetic molecular theory of gases.