4.4 Gas Law

MODUL PDP SPM
PASCA PKP
NEGERI PERAK
2020

PHYSICS Form 4

4.4:

Gas Laws

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4.4 Gas Laws

Learning Standard:

Pupils are able to:

• explain pressure, temperature and volume of gas in terms of the behaviour of gas
molecules based on the Kinietic Theory of Gas.

• experiment to determine the relationship between the pressure and volume of a
fixed mass of gas at constant temperature.

• experiment to determine the relationship between the volume and temperature of a
fixed mass of gas at constant pressure.

• experiment to determine the relationship between the pressure and temperature of
a fixed mass of gas at constant volume.

• solve problems involving pressure, temperature and volume for a fixed mass of gas
using Gas Law formulas.

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Note: 4.4 Gas Laws

PRESSURE, TEMPERATURE AND VOLUME OF GAS

1. Based on the Kinetic Theory of Gas :
a) Gas molecules are very small and far apart from one another.
b) Gas molecules are in constant random motion and constantly colliding with each
other.
c) The collision of gas molecules with each other and with the wall of container is
elastic.

2. Table below shows the characteristics of gas based on the Kinetic Theory of Gas.

Characteristic Description
Volume (m3)
• Gas molecules moves FREELY AND RANDOMLY and fill the entire
Temperature (K) space of the container.

Pressure (Pa) • Volume of gas = Volume of its container

• Gas molecules are in constant RANDOM MOTION and have
AVERAGE KINETIC ENERGY that INCREASES WITH
TEMPERATURE.

• The higher the temperature, the higher the motion of molecules.

• Gas molecules are in constant RANDOM MOTION and COLLIDE
WITH THE WALL OF THE CONTAINER and REBOUND.

• For each molecule, there is CHANGE IN MOMENTUM and there
is a FORCE acting on the wall of container.

• Force per unit area = Pressure of Gas

RELATIONSHIP BETWEEN PRESSURE AND VOLUME OF GAS

(constant mass, m and Pressure, P increases,
constant temperature, T. Volume, V decreases.

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For a fixed mass of gas,
PRESSURE of gas is INVERSELY PROPORTIONAL to the VOLUME

if TEMPERATURE of gas remains constant.

P1 Low P2 High
V1 High V2 Low

∝ 1 BOYLE’S LAW

=
= constant

1 1 = 2 2

Graph of relationship between pressure and volume of gas

P against V P against PV against V


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Example :

Air in a closed syringe has a volume of 100 cm3 and pressure of 110 kPa. The piston of the
syringe is pushed to compress the air to a volume of 68 cm3. Calculate the pressure of the
compressed air.

Solution :

Step 1 : List the given information in symbols.

P1 = 110 kPa

P2 = compressed air pressure
V1 = 100 cm3
V2 = 68 cm3

Step 2 : Identify and write down the formula used.

Temperature of gas does not change.

Boyle’s Law formula is used.

1 1 = 2 2

Step 3 : Substitute numerical values into the formula and perform the calculations.

110 × 100 = 2 × 68

2 = 110 × 100
68

2 = 161.76

RELATIONSHIP BETWEEN VOLUME AND TEMPERATURE OF GAS

Temperature, T increases,
volume, V increases

(Mass, m is fixed and pressure, P is constant)

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For a fixed mass of gas,
VOLUME of gas is DIRECTLY PROPORTIONAL to absolute temperature

if PRESSURE of gas remains constant.

V1 Low V2 High

T1 Low T2 High
∝
CHARLES’ LAW

=


= constant

1 = 2
1 2
Cold water Boiling water

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Graph of relationship between volume and temperature

Graph of V against θ in the unit of degree Celsius Graf of V against T in the unit of Kelvin

extrapolation

θ/ °C

T = (θ + 273) K

Absolute zero = -273 °C = 0 K

THE LOWEST TEMPERATURE possible, in which
GAS MOLECULES NO LONGER MOVE and
UNABLE TO FILL THE SPACE.

Example :

An air bubble has a volume of 1.5 cm3 at a temperature of 27oC. What is the volume of the air
bubble if its temperature increases to 37oC.

Solution :

Step 1 : List the given information in symbols.

V1 = 1.5 cm3

V2 = Final volume of air

T1 = (27 + 273) K = 300 K

T2 = (37 + 273) K = 310 K

Step 2 : Identify and write down the formula used.

Gas pressure is constant.

Charles’ Law formula is used.

1 = 2
1 2

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Step 3 : Substitute numerical values into the formula and perform the calculations.

1.5 = 2
300 310

2 = 1.5 × 310
300

2 = 1.55 3

RELATIONSHIP BETWEEN PRESSURE AND TEMPERATURE OF GAS

For a fixed mass of gas,
PRESSURE of gas is DIRECTLY PROPORTIONAL to ABSOLUTE TEMPERATURE

if VOLUME of gas remains constant.

P1 Low P2 High

T1 Low T2 High

GAY-LUSSAC’S LAW

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∝ =


= constant

1 = 2
1 2

Graph of relationship between pressure and temperature
Graph of P against θ in the unit of degree Celsius Graph of P against T in the unit of Kelvin

extrapolation

θ/ °C

Example :
Gas in a closed steel cylinder has a pressure of 200 kPa at a temperature of 25°C. What is the
gas pressure when the cylinder is heated to a temperature of 62°C?
Solution :
Step 1 : List the given information in symbols.
P1 = 200 kPa
P2 = final pressure of air
T1 = (25 + 273) K = 298 K
T2 = (62 + 273) K = 335 K

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Step 2 : Identify and write down the formula used.

Volume of gas is consant.

Gay-Lussac’s Law formula is used.

1 = 2
1 2

Step 3 : Substitute numerical values into the formula and perform the calculations.

200 = 2
298 335

2 = 200 × 335
298

2 = 224.83

BOYLE’S LAW 1 1 = 2 2

1 = 2 1 = 2
1 2 1 2

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4.4 MIND MAP

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4.4 FAQ

No Question And Answer
1Q What are gas laws?

A Gas laws are laws that relate the pressure, volume, and temperature of a
2Q gas.

A What causes gas pressure?

3Q Gas pressure is caused when gas particles hit the walls of their container.
A The more often the particles hit the walls, and the faster they are moving
when they do this, the higher the pressure. This is why the pressure in a tyre
4Q or balloon goes up when more air is pumped in.
A
Why does the pressure of a gas sample increase when the temperature is
5Q increased at constant volume?
A
As the temperature increases, the average kinetic energy increases as does
6Q the velocity of the gas particles hitting the walls of the container. The force
A exerted by the particles per unit of area on the container is the pressure, so
as the temperature increases the pressure must also increase.

What are the three simple gas laws?

The gas laws consist of three primary laws: Charles' Law, Boyle's Law and
Pressure Law (all of which will later combine into the General Gas Equation
and Ideal Gas Law).

What are the applications of Boyle's Law?

One practical application of Boyle's law is drawing fluid into a syringe. Pulling
back on the plunger increases the interior volume of the syringe and reduces
its pressure. The fluid outside the syringe is sucked into the barrel until the
interior and exterior pressure are balanced.

What is a good example of Charles Law?

One easy example of Charles' Law is a helium balloon. If you fill a helium
balloon in a warm or hot room, and then take it into a cold room, it shrinks
up and looks like it has lost some of the air inside. But if you take it back to a
warm or hot place, it fills back up and seems to be full again.

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4.4 EXERCISE

SECTION A
1. Diagram shows pressure in a tyre before a car starts it’s journey

210 kN m-2

The pressure in the tyre increased to 212.0 kN m-2 after a long journey.
This is caused by

[MEMAHAMI]
A the density of air inside the tyre which has decreased
B the mass of air inside the tyre which has increase
C the mass of air inside the tyre which has decrease
D the temperature inside the tyre which has increased

2 The air pressure in a car tyre is 210 kPa at a temperature of 27oC. What is the air
pressure in the tyre when the temperature is 37oC?
[Assume the volume of the air in the tyre is constant]
[MENGAPLIKASI KUANTITATIF]
A 141 kPa
B 201 kPa
C 217 kPa
D 311 kPa

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3. An experiment is carried out to investigate the changes of pressured with the
temperature for a fixed mass of gas in conical flask.
Which of the following graphs shows the correct relationship between pressure
and temperature?

[MENGETAHUI]

4. Before a long journey, the air in a tyre of a lorry has a pressure of 128 kPa and a
temperature of 27°C. After the journey the air pressure in the tyre is 132 kPa.
Which expression determines the temperature of the air in the tyre after the
journey?
[Assume the volume of the tyre is constant]

[MENGAPLIKASI KUANTITATIF]

A 132 × 27 °C
 128 

B 128 × 27 °C
 132 

C  132 × 300  − 273°C
128 

D  128 × 300  − 273°C
132 

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5. Which graph shows the relationship between the pressure, P and the volume, V
of a fixed of gas at constant temperature?
[MENGETAHUI]

SECTION B

6. Diagram 6.1 and Diagram 6.2 show an experiment to study the relationship between
volume and pressure of air trapped in a closed syringe.

Bourdan Gauge Bourdan Gauge
Tolok Bourdon Tolok Bourdon

Piston Piston
Piston Piston
0
0

Diagram 6.1 Diagram 6.2

(a) State the function of Bourdon Gauge.

[MENGETAHUI]

……………………………………………………………………………………………………………….
[1 mark]

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(b) Based on Diagram 6.1 and 6.2, compare: [MENGANALISIS]
(i) The volume of the gas in the syringe.

...........................................................................................................
[1 mark]

(ii) The reading of Bourdon Gauge.

...........................................................................................................
[1 mark]

(iii) The temperature of the gas in the syringe.

...........................................................................................................
[1 mark]

(c) Using your answer in 6(b)(i) and 6(b)(ii), state a relationship between the volume of
gas and the reading of Bourdon Gauge.
[MENGANALISIS]

......................................................................................................................................
[1 mark]

(d) Name a physics law involved in the above observation.

[MENGETAHUI]

......................................................................................................................................
[1 mark]

(e) By using The Molecular Kinetic Theory, explain your answer in 6(c).
[MEMAHAMI]

......................................................................................................................................
[2 mark]

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7. Diagram 7.1 shows the reading of the Bourdon Gauge is 1.1 kPa before the piston of the
bicycle pump is pushed inward and the volume of air trapped inside the pump is 0.4m3.

Diagram 7.1
Diagram 7.2 shows the reading of the Bourdon Gauge is 2.2 kPa when the piston of the
bicycle pump is pushed inwards.

Diagram 7.2
(a) Based on Diagram 7.1, tick ( √ ) the correct answer in the provided box.

[MENGETAHUI]
Bourdon Gauge can measure

gas temperature
gas pressure

(1 mark)

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(b) Based on Diagram 7.1 and Diagram 7.2
[MENGANALISIS]

(i) compare the number of air particles inside the bicycle pump.

...........................................................................................................
[1 mark]

(ii) Sketch a pressure-volume graph of the situations in Diagram 7.1 and Diagram
7.2.

Pressure
Tekanan

Volume
Isipadu

(c) Calculate the volume of air trapped in the bicycle pump in Diagram 7.2.
[MENGAPLIKASI KUANTITATIF]

[2 marks]

(d) (i) Based on the answer in 7(b), what happens to the kinetics energy of the air
particles when the air is compressed.
[MEMAHAMI]

......................................................................................................................................

(1 mark)

(ii) Give one reason for the answer in 7(d)(i).

......................................................................................................................................
(1 mark)

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QR CODE QR CODE

4.4 Gas Laws

Title link

4.4 GAS LAWS https://youtu.be/TtEF3ypEt1s
( BOYLE'S LAW)

4.4 GAS LAWS https://youtu.be/D4QALuHBEyo
(CHARLE'S LAW)

4.4 GAS LAWS https://youtu.be/TlMQ8TgoCBM
(GAY-LUSSACS
LAW)

Measuring the https://youtu.be/LbZkFuJn_S4
specific latent heat
of vaporization of
water

REINFORCEMENT https://drive.google.com/file/d/15DHHxRcnsFdDRRpldrGHwl
TEST cWH_brIEQB/view?usp=sharing

ANSWER https://drive.google.com/file/d/1dkAL0CXHYKk1KyN26d7oM
REINFORCEMENT mdvUMPEOocA/view?usp=sharing
TEST

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4.4 ANSWER

Section A

1D
2C
3B
4C
5D

Section B

6. (a) To measure gas pressure

(b) (i) Volume of gas in Diagram 6.1 is higher

(ii) The reading of Bourdon Gauge in 6.1 is less

(iii) Temperature is constant

(c) When the volume of gas decreases the reading of Bourdon Gauge increasing

(d) Boyle’s Law

(e) - When the volume of gas decreases, the rate of collision of gas particles per unit
area increases

- The pressure of gas will increase

7.(a) Gas Pressure

(b)(i) Same
Pressure

(ii)

Volume

(c) 1.1 x 0.2 = 2.2V2
V2 = 0.1m3 (answer with correct unit)

(d) (i) Same // Remains unchanged
(ii) Constant // Same temperature // speed of gas particles

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