NB: When a body is heated its mass does not change, ie m1 = m2 =m  
ퟏ
ퟏ
(흆 흆 )  
ퟏ− ퟐ  
−
(
)
(
)
ퟐ
흆
흆
ퟏ
흆 흆  
ퟏ ퟐ  
흆
흆
흆
흆
흆
ퟏ
ퟏ−  
ퟐ
ퟏ−  
ퟐ
휸 =  
=
=
=
ퟏ
ퟏ
×(푻 −푻 )  
×(푻 −푻 )  
흆 흆 (푻 −푻 )  
흆 (푻 −푻 )  
ퟐ
ퟐ
ퟏ
ퟐ
ퟏ
ퟏ
ퟐ
ퟐ
ퟏ
ퟐ
ퟏ
흆
ퟏ
흆
ퟏ
(흆 흆 )  
ퟏ−  
ퟐ
휸 =  
(
)
(
)
→ 휸흆ퟐ 푻ퟐ − 푻ퟏ = 흆ퟏ−흆ퟐ  
흆 (푻 −푻 )  
ퟐ
ퟐ
ퟏ
흆
ퟏퟑ.ퟔ  
ퟏ
=
=
(
)
휸흆ퟐ 푻ퟐ − 푻ퟏ + 흆ퟐ = 흆ퟏ → 흆ퟐ  
−ퟒ  
휸(푻 −푻 )+ퟏ  
ퟏ.ퟖퟐ×ퟏퟎ ×ퟓퟎ+ퟏ  
ퟐ
ퟏ
0
3
( )  
∴ 풕풉풆 풅풆풏풔풊풕풚 흆ퟐ 풐풇 풎풆풓풄풖풓풚 풂풕 50 C is 13.48 g/cm  
11. Describe an experiment to show that same volume of different liquids heated to same rise  
in temperature expand by different amounts.  
ANS;  
•
Just like solids, liquids expand at different rates. In order to investigate this, a number of  
identical flasks are filled with different liquids ensuring that their initial levels are the same in  
the glass tubes. For a fair comparison, the tubes should be identical i.e. of same diameter.  
The flasks are then simultaneously immersed in a bath of hot water. The bath of water  
should be stirred continuously to ensure that temperature is uniform.  
•
It will be observed that the level of the liquids in the tubes differ after some time. If water,  
alcohol and methylated spirit were used, it would be observed that methylated spirit  
expanded the most, followed by alcohol and water the least.  
Thermal Expansion in Gases  
•
•
Gases expand much more than solids and liquids when heated.  
This is because the particles in gases are not held closely together, as they are in solids and  
liquids, but are instead free to move in all directions.  
•
•
Three  
properties  
are  
important  
when  
studying  
the  
expansion  
of  
gases.  
These include Pressure, Volume and Temperature.  
The temperature must be converted into Kelvin scale  
Charles’ Law  
•
This law involves the relationship between the volume and the temperature of a fixed mass of a  
gas at constant pressure. The law state that  
“
The volume of a fixed mass of a gas is directly proportional to the absolute temperature  
provided the pressure remains constant  
”
•
•
This means that if volume increases, the temperature will also increase.  
For example; Hot air rises, which is why hot-air balloons ascend through the atmosphere and why  
warm air collects near the ceiling and cooler air collects at ground level. Because of this  
behavior, heating registers are placed on or near the floor, and vents for air-conditioning are  
placed on or near the ceiling. The fundamental reason for this behavior is that gases expand  
when they are heated. See the figure below  
•
Mathematically  
푽
푻
V
∝
T
→V= kT ………………… make K the subject  
푲 =  
푽ퟏ  
푻ퟏ  
푽ퟐ  
푻ퟐ  
푽ퟏ  
푽ퟐ  
푻ퟏ  
푻ퟐ  
=
→
=
Whereby  
:
V1 = initial volume  
T1 = initial temperature  
V2 = final volume  
T2 = final temperature  
Graphical Representation of Charles law  
•
Graph between Volume and absolute temperature of a gas at constant pressure is a "straight  
line" .This graph shows that at constant pressure, the volume of the given sample of the gas is  
directly proportional to the Kelvin temperature.  
If the graph between V and T is extra plotted, it intersects T-axis at -273 C. At -273 C volume  
of any gas theoretically becomes zero as indicated by the graph.  
0
0
•
•
From the graph above it seems that as temperature increases also volume increases and  
vice versa  
•
•
•
The graph does not pass through the Celsius temperature origin (0 ºC). If they are produced  
backward they cut the temperature axis at about –273 ºC. This means at 0 ºC the volume of  
the gas is non-zero, but at –273 ºC the volume of the gas touches the zero mark.  
This temperature (–273 ºC) is called absolute zero because it is found to be the lowest  
temperature possible. It is the zero of the absolute or Kelvin scale of temperature. Degrees  
on this scale are called kelvin and are denoted by K.  
But practically volume of a gas can never become zero. Actually no gas can achieve the  
0
lowest possible temperature and before -273.16 C all gases are condensed to liquid. This  
0
temperature is referred to as absolute scale or absolute zero. At -273.16 C all molecular  
motions are ceased.  
•
Absolute zero is the temperature at which all particles of matter possess zero energy  
The figure below shows the relationship between the Kelvin scale and the Celsius scale of  
temperature  
Conversion;  
0
( )  
푻 푲 = ퟐퟕퟑ + 휽 ( C) .................... 1  
0
( )  
휽 ( C) = 푻 푲 − ퟐퟕퟑ........................2  
Worked Examples:  
1. A gas of volume 300 cm3 was heated from 230 C to 830 C. Determine the volume at one  
atmospheric pressure  
Solution:  
Given: T1 = 230 C = 23+273 = 296 K, T2 = 870 C = 87 + 273 = 360 K  
V1 = 300 cm3, V2 =?  
푻
푻
ퟏ
푽ퟏ  
From:  
=
푽
ퟐ
ퟐ
푽 × 푻  
ퟑퟔퟎ 풙 ퟑퟎퟎ  
ퟐퟗퟔ  
ퟏ
ퟐ
= ퟑퟔퟒ. ퟖퟔcm3  
푻
푽
ퟏ
ퟏ
=
=
→ 푽  
=
ퟐ
푽
ퟐ
푻
ퟐ
푻
ퟏ
2. To what temperature must a gas at 1270C be cooled, so that its volume is reduced to 1/5 of its  
initial volume? Assume pressure remains constant. [ANS: 80 K or - 1930 C]  
= 푽, 푻ퟏ  
ANS; 푽ퟏ = 푽, 푽ퟐ  
=
1270C = 127+273 = 400K, T2 =?  
ퟓ
ퟒퟎퟎ  
ퟓ
푻
ퟏ
푽
ퟒퟎퟎ  
푽ퟏ  
→ ퟓ푻 = ퟒퟎퟎ → 푻 =  
= ퟖퟎK  
From;  
=
→
=
푽/ퟓ  
푻
푽
ퟐ
푻
ퟐ
Significance of Charles’ Law  
•
It explains how gases behavior at constant pressure and the relation between the absolute  
temperature and the volume of the gas. According to Charles law, at a constant pressure, the  
volume and absolute temperature of a gas are directly proportional to each other  
At constant pressure, the density of a gas is inversely proportional to its volume, ie,.. 흆 휶  
•
•
ퟏ
푻
Using this concept hot air is used to fill the balloons used for meteorological purposes  
Real life examples of Charles law  
•
Charle’s Law describes the expansion of gases when they are heated. Keeping it simple, we  
can say that as the temperature of any particular gas increases, the molecules in that gas  
exhibit increased movement. As soon as the movement of the molecule increases, there is an  
increased number of collisions. What happens is that the molecules begin to hit the walls of the  
container more frequently, and, that too, with an increased amount of force.  
•
If the wall of the container is flexible, say, a balloon, the pressure will remain constant; thereby,  
allowing the volume to increase. However, if the container is inflexible, the more frequent  
collisions will result in increased pressure. In this article, we will talk about the real-life  
examples of Charle’s Law..  
(i)  
It is a common observation that an inflated basketball shrinks in size when left  
under a cold environment. This is true because a decrease in temperature results into a  
corresponding decrease in volume according to Charles’s Law. Therefore, the volume of  
air inside the basketball shrinks on cold day.  
(ii)  
Tyre. In cold weather, you might have regularly kept a check on the pressure of the  
tyres of your car. Driving increases the temperature of the tyres, and, therefore, the air  
inside the tyre warms and expands. When you measure the pressure of the tyres at the  
time when you have just driven the car, it will be high. However, in cold weather, the  
pressure of the tyres will be low. So, it is recommended that you should measure the  
pressure of the tyres regularly in colder climates, especially before long trips or  
during cold snaps  
.
(iii)  
Explosion of Aerosols: Aerosols refers to products like insecticides, perfumes,  
deodorants, spray paints and so on. If aerosol bottle is exposed to a very high  
temperature, it may explode. This is true because when heated, the pressurized gas  
expands and increases in volume. Since the gas cannot escape from its locked nozzle, it  
eventually explodes. In fact, this is the reason behind the warning signs on its  
container, indicating that it should be stored in a cool environment, and kept away from  
the sunlight and high temperature  
(iv)  
(v)  
Turkey Timer. The working of the Pop-Up Turkey Timer (Thermometer) is also based on  
Charle’s law. Let’s see how! If you remember what the Charle’s law states, you might be  
familiar with the fact that gases expand when heated. The same principle applies to the  
Pop-Up Turkey Timer. The thermometer (or timer) is placed inside the turkey. As the  
temperature increases and the turkey cooks, the gas inside the thermometer also  
expands. As soon as the timer pops, it indicates that the turkey has been cooked.  
Helium Balloon. If you have had the chance to go out on a chilly day, you might have  
noticed that the balloon crumbles. However, if you take the balloon to a warm room, it  
regains its shape. Why does this happen? This happens because the temperature on a  
cold day is low, and, so, the volume decreases. Now, in accordance with the Charle’s  
Law, as soon as you enter a warm room, the temperature increases; with an increase in  
temperature, the volume also increases. Therefore, the balloon goes back to its original  
shape.  
(vi) Bakery. Charle’s Law finds its way into our kitchens as well. In case you have ever tried  
your hand at baking, you might be familiar with the substance most commonly used in  
cooking, i.e., the yeast. Yeast is often used in baking to make the bakery products fluffy.  
Yeast is responsible for releasing carbon dioxide bubbles. These carbon dioxide bubbles  
expand further with high temperature. The expansion of the carbon dioxide bubbles with  
an increase in temperature works as a leavening agent and cause the bakery products to  
become fluffy.  
(vii) Hot Air Balloon. You might have wondered about the working of the hot air balloon.  
Charle’s Law describes that temperature and volume are directly proportional to each  
other. When a gas is heated, it expands. As the expansion of the gas takes place, it  
becomes less dense and the balloon is lifted in the air. The warm air is less dense than  
the cold air, which means that it is lighter than the cold air.  
Class Activity – 6:5  
1. Use Charles’s law to explain why cooler air sinks.  
2. Change the following temperatures to Kelvin scale (a) 33°C (b) 57°C  
ANS:  
(a) T (K) = 306 K  
(b) T (K) = 330 K  
3. Change the following temperatures to Celsius scale (a) 4K (b) 292K  
ANS: (a) θ° C = - 269°C  
(b) θ° C = 19°C  
A 0.20m3 container with a movable piston holds nitrogen gas at a temperature of 20°C. What  
4.  
will be the volume of the gas if the temperature increased to 50°C? (ANS: V2 = 0.22 m3)  
5. (a)What  
is  
the  
need  
for  
the  
Kelvin  
scale  
of  
temperature?  
(b) What is the boiling point of water on the Kelvin scale? Convert it into centigrade scale.  
ANS;  
(a) The behaviour of gases shows that it is not possible to have temperature below 273.15C.  
This act has led to the formulation of another scale known as Kelvin scale. The real  
advantage of the Kelvin scale is that it makes the application and the use of gas laws  
simple. Even more significantly, all values on the Kelvin scale are positive  
(b) 373K, 1000C  
A gas occupies a volume of 20 cm3 at 27°C and at normal atmospheric pressure. Calculate the  
new volume of the gas if it heated to 54°C at the same pressure.  
A gas occupies 3 litres at 0°C. What volume will it occupy at -20°C, pressure remaining  
6.  
7.  
(ANS: V2 = 21 cm3)  
constant? [ANS; 2.78L]  
8. A gas occupies 500 cm3 at normal temperature. At what temperature will the volume of the gas  
be reduced by 20% of its original volume, pressure being constant? [ANS; 218.4K or -52.60C]  
Boyle’s Law  
•
This law involves the relationship between the volume and the pressure of a fixed mass of a  
gas at constant temperature. The law state that  
“The volume of fixed mass of a gas is inversely proportional to its pressure if the  
temperature is kept constant”  
•
T
he figure below shows the demonstration of Boyles’ Law by diagram  
•
•
Mathematically  
P∝ ퟏ  
→ P = 푲  
→ PV= 퐾  
→ PV = Constant  
푽
푽
∴ 푷ퟏ푽ퟏ = 푷ퟐ푽ퟐ  
Whereby:  
푷ퟏ = initial pressure  
푽ퟏ= initial volume  
푷ퟐ = final pressure  
푽ퟐ= final volume  
The equation above shows that as the pressure increases, the volume decreases and vice  
versa. For example, when the pressure doubles, the volume is decreased by half. Also, the  
units of pressure and volume must be consistent. P1 and P2 must be expressed in Pa or atm.  
V1 and V2 must be expressed in m3 or L.  
Graphical representation of Boyles’ Law  
:
•
A
graphical representation of Boyles’ law is typically seen as a curve. This curve is called the  
PV (Pressure  
–
Volume) curve, and it is hyperbolic in nature. It shows the relationship  
between the pressure of a gas and its volume at constant temperature.  
•
•
From the graph above it seems that as pressure increases also volume decreases and vice  
versa.  
The figure below shows the relationship between reciprocal of volume and pressure  
•
From the graph above it seems that as the pressure increased also inverse of volume  
increased and vice versa  
Worked Examples  
1. A gas occupies 250 cm3 when the pressure is 20 atmospheres. What will its volume be if  
pressure is reduced to 15 atmospheres while the temperature is kept constant?  
Answer  
P1 = 20 atm, P2 = 15 atm, V1 = 250, cm3 V2 = V2  
From: P1 V1 = P2 V2  
ퟓퟎퟎퟎ  
= ퟑퟑퟑ. ퟑퟑ cm3  
=
20 x 250 = 15 x V2  
→ 푽ퟐ  
ퟏퟓ  
2.  
A bubble of air has a diameter of 2.0mm when it is 0.5 m below the water surface of a  
boiler, calculate the diameter of the bubble as it reaches the surface, assuming that the  
temperature remains constant. Take g = 10m/s2, density of water = 1000kg/m3 and  
atmospheric = 105 Nm-2  
ANSW: Given, d1 = 2.0mm, h = 0.5m, g = 10 m/s2, 휌 = 1000kg/m3,  
P1 = P2 + P (due to column of water) = P2 + 휌ℎ푔  
P1 = 105 + 0.5 x 1000 x 10 = 10= 1.05 x 105 Nm -2, P2 = 105 Nm-2  
ퟑ
ퟒ흅푹  
•
From Boyle’s Law: P1V1= P 2V 2, but assume that the bubble is spherical, then V =  
, But;  
ퟑ
R = d/2 =2/2 =1  
P1V1 = P2V2 → 푷ퟏ ×  
ퟑ
ퟏ
ퟑ
ퟐ
ퟒ흅푹  
•
= 푷ퟐ × ퟒ흅푹 → 푷ퟏ × 푹ퟑ = 푷ퟐ × 푹ퟑ  
ퟏ
ퟐ
ퟑ
ퟑ
ퟑ
ퟓ
ퟑ
ퟑ
ퟑ
푷 ×푹  
푷
ퟏ
ퟏ.ퟎퟓ×ퟏퟎ  
ퟏ
ퟏ) = 푹ퟏ √(  
√
) = ퟏ × (  
√
) = 1.0164 mm  
•
•
푹ퟐ = (  
ퟓ
ퟏퟎ  
푷
ퟐ
푷
ퟐ
Therefore; diameter of bubble as it reaches the surface of water  
d2 = 2R2 = 2 x 1.0164 = 2.033 mm  
3. A gas is expanded, at a constant temperature, from a volume of 500 mL to a volume of 1.5  
litre, where its final pressure is 150 mm of Hg. What was the original pressure? A; 450 mmHg]  
[
4. Find the volume of a sample of nitrogen at a pressure of 1.50 atm, if its volume is 3.15 L at  
1.00 atm and the temperature is constant. [ANS; 2.1L]  
Significance of Boyle’s Law  
•
It explains how gases behavior at constant temperature and the relation between the pressure  
and the volume of the gas. According to Boyle’s law, at a constant temperature, the  
pressure and volume of a gas are inversely proportional to each other  
•
•
At constant temperature, the density of a gas is directly proportional to its pressure, ie,..  
P
휶 흆  
Atmospheric pressure is low at high altitudes, so air is less dense. Hence, a lesser  
quantity of oxygen is available for breathing. This is the reason why mountaineers have to  
carry oxygen cylinders with them.  
•
•
It explains how people breathe and exhale air. When the diaphragm expands and contracts,  
lung volume increases and decreases, changing the air pressure inside of them. The pressure  
difference between the interior of the lungs and the external air produces either inhalation or  
exhalation  
Doubling pressure halves volume, at constant temperature and mass. Example: When you  
blow bubbles underwater, they expand as they rise to the surface.  
Class Activity – 6:6  
1. Use Boyle’s law to explain why it is dangerous to heat even a small quantity of water in a sealed  
container.  
2.  
A gas in a cylinder occupies a volume of 465 ml when the pressure on it is equivalent to 725 mm  
of mercury. What will be the volume of the gas when the pressure on it rises to 825 mm of mercury  
while the temperature is held constant? (ANS: V2 = 408.6 ml)  
Bubble of gas, which has a volume of 0.4 cm3, released by a diver 30 m in under the surface of a  
lake, what will be the volume of the bubble when it reaches the surface? (Assume the barometric  
pressure is 10 m of water.) (ANS: V2 = 1.2 cm3)  
3.  
4. Sketch a graph of the volume of a gas versus the pressure on the gas. What would the graph  
of V versus P look like if volume was directly proportional to pressure?  
5. What will be the minimum pressure required to compress 500 dm3 of air at 1 bar to 200  
dm3 temperature remaining constant. [ANS; 2.5 bar]  
6. A steel cylinder of internal volume 20 litres is filled with hydrogen at 29 atmospheric pressure. If  
hydrogen is used to fill a balloon at 1.25 atmospheric pressure at the same temperature, what  
volume will the gas occupy? [ANS; 464 L]  
7. 2 litres of a gas is enclosed in a vessel at a pressure of 760 mmHg. If temperature remains  
constant, calculate pressure when volume changes to 4 dm3. [ANS; 380mmHg]  
8. 800 cm3 of gas is collected at 650 mm pressure. At what pressure would the volume of the gas  
reduce by 40% of its original volume, temperature remaining constant? [ANS; 1083.33 mmHg]  
9. A cylinder of 20 litres capacity contains a gas at 100 atmospheric pressure. How many flasks of  
200 cm3capacity can be filled from it at 1 atmosphere pressure, temperature remaining constant?  
ANS; N = 10,000 flasks.  
10. Why Boyles’ law is important?  
ANS; Boyle’s law explains the behaviour of gases. It proves that the pressure and volume of a gas  
are inversely proportional. When pressure is applied to a gas, the volume shrinks and the pressure  
rises.  
11. 88 cm3 of nitrogen is at a pressure of 770 mm mercury. If the pressure is raised to 880 mmHg, find  
by how much the volume will diminish, temperature remaining constant.  
[
푽′ = 푽ퟐ − 푽ퟏ = ퟏퟏcm3]  
Application of Boyle’s Law  
•
Bubbles in water seem to grow as they ascend from the bottom of the water to the  
surface .This is due to the decrease in Pressure  
•
Death of deep sea creatures when brought to shallow waters .This happens when the  
pressure inside their bodies is greater than the pressure of the surrounding water hence the  
balance is distracted causing a burst of the cells bladders and other internal biological  
structures due to increase in volume  
•
•
Popping of ears at high altitude. When the plane starts to rise it is going from an area of  
high pressure where your ears are accustomed to an area of low pressure causing the air  
inside increases in volume, this straining your eardrums  
The operation of your lungs also can be explained using Boyle’s Law. When you  
inhale (breathe in), your diaphragm expands the volume of the lungs, causing a pressure  
drop that allows outside air to rush into the lungs (inhalation). When you exhale (breathe  
out), your diaphragm are relaxing, thus reducing the volume inside your lungs, increasing  
the pressure and forcing the air outwards.  
•
•
Soda bottles or cans are consider a practical application of Boyle’s law, as all of us  
apply Boyle’s Law but unintentionally. Note that when you open the bottle of soda quickly, the  
gas rushes from everywhere in the form of foam, causing a mess. So what is the cause of  
this mess? This mess occurs because the soda is pumped into the soda bottle by passing the  
water on carbon dioxide. When you open the bottle, you are actually reducing the  
pressure on the gas, and the volume of the gas expands. If you remove the cap  
quickly, the gas pushes out of the bottle. Therefore, you should open the cap slowly  
and carefully until the gas comes out quietly.  
The working of a syringe can also be explained using Boyle’s Law. When  
the plunger of a syringe is pulled out, the volume inside the barrel increases, resulting in a  
decrease in the pressure inside the barrel. Fluids (such as water) flow from a high pressure  
area to a low pressure area. This means that once the pressure inside a syringe is lower  
than the pressure outside the syringe, a fluid near the needle (e.g., water, medicine, etc.)  
will flow into the syringe. The opposite is also true. When the plunger is pushed back in, the  
volume decreases and the pressure increases. Once the pressure is greater than that  
outside the syringe, the fluid inside the barrel will flow out.  
Pressure Law (Gay Lussac's Law)  
•
This law involves the relationship between the temperature and the pressure of a fixed mass  
of a gas at constant volume. The law states that  
“
At constant volume, the pressure of a fixed mass of a gas is directly proportional to  
its absolute temperature  
”
•
For example; If you heat a gas you give the molecules more energy so they move faster. This  
means more impacts on the walls of the container and an increase in the pressure.  
Conversely if you cool the molecules down they will slow and the pressure will be decreased.  
See the figure below  
•
Mathematically  
푷
푻
→
푷 ∝ 푻  
→ P= K T  
= 푪풐풏풔풕풂풏풕  
푷ퟏ  
푷ퟐ  
푻ퟐ  
푷ퟏ  
푻ퟏ  
푻ퟐ  
∴
=
→
=
푻ퟏ  
푷ퟐ  
Where:  
P1 = initial pressure, T1 = initial temperature  
P2 = final pressure, T2 = final temperature  
Graphical representation of Gay Lussac's Law  
:
•
From the graph above it seems that as pressure increases also temperature increases and  
vice versa  
Worked Examples  
1. A vessel used for storing gas has a safety valve which blows off at 106N/m2. It contains gas at a  
pressure of 8.0 x 105 N/m2 at 15°C. At what temperature would the valve start to blow off?  
[ANS: 360K or 870C]  
ANS;  
푷ퟏ = ퟏퟎퟔNm-2, 푷ퟐ = ퟖ × ퟏퟎퟓNm-2, T2 = 150C = 273+15= 288K, T1 =?  
ퟔ
ퟔ
푻
ퟏퟎ  
푻
ퟏퟎ × ퟐퟖퟖ  
ퟏ
푷ퟏ  
From:  
=
→
=
→ 푻 =  
= 360K  
ퟓ
ퟓ
ퟖ×ퟏퟎ  
ퟖ×ퟏퟎ  
ퟐퟖퟖ  
푷
ퟐ
푻
ퟐ
2. A car tyre is at an air pressure of 4.0 x 105 Pa. at a temperature of 270 C. While it is running, the  
temperature rises to 750 C. What is the new pressure in the tyre? (Assume the tyre does not  
expand)  
Answer  
Since the tyre does not expand, this implies that the volume is constant  
P1 = 40 000Pa, P2 = P2,  
T1 = (27+273) = 300K, T2 = (75 + 273) =384 K  
푻
ퟒퟎퟎퟎퟎ  
푷
ퟑퟎퟎ  
ퟑퟖퟒ  
ퟒퟎퟎퟎퟎ × ퟑퟖퟒ  
ퟏ
푷ퟏ  
From:  
=
51,200 Pa  
=
→
=
→ 푷 =  
ퟑퟎퟎ  
푷
ퟐ
푻
ퟐ
Significance of Pressure Law (Gay Lussac’s Law)  
Pressure in well-inflated tyres of automobiles is almost constant. But on a hot summer day, this  
increases considerably and the tyre may burst if pressure is not adjusted properly  
•
.
Similarly, during winters, on a cold morning, we find the pressure in the tyres of a vehicle  
decreased considerably.  
Real life examples of Gay Lussac’s Law (Pressure law)  
(i) Pressure cooker: Applying heat to a pressure cooker increases the pressure inside the device.  
Increasing pressure raises the boiling point of water, shortening cooking times. Because  
the container is sealed, flavors aren’t lost to the air with steam When a pressure cooker is  
kept on a heating source (stove). As per Gay-Lussac's law, the pressure of the fluid in the  
cooker increases with the rising of the temperature.  
(ii)  
Aerosol can: The reason you shouldn’t store aerosol cans under hot conditions or dispose  
of them by burning is because heating the can increases the pressure of its contents,  
potentially causing the can to burst.  
(iii)  
Gun bullet. When the bullet from a gun is ignited, the chemical energy stored in the shell of  
the bullet is converted into heat by chemical reactions. This heat increases the temperature  
which as per Gay-Lussac's law increases the pressure. Because of the high pressure, the  
bullet is fired from the gun.  
(iv)  
(v)  
Automobile tyres. The rupture of automobile tyres on subjection to high temperature is a  
classic example of Gay-Lussac's law. The high temperature pressurizes the air inside the  
tyres and beyond a point, they explode.  
Soda or soft drinks bottles are made of thick glass. This is because, when gas is heated  
in a closed container its pressure increases .Hence they are made of thick glass to  
withstand pressure increase.  
NB;  
Gay-Lussac’s law is very similar to Charles’s law, with the only difference being the type of  
container. Whereas the container in a Charles’s law experiment is flexible, while it is rigid in a  
Gay-Lussac’s law experiment  
Class Activity – 6:7  
1. A rigid metal container holds carbon dioxide gas at a pressure of 2 x 105 Pa and a temperature of  
30°C. What temperature the gas be lowered for the pressure to reduce to half (1 x 105 Pa)?  
ANS: T2 = 151.5K = -121.5°C  
2.  
A gas in a fixed-volume container has a pressure of 1.6 x 105 Pa at a temperature of 27°C. What  
will be the pressure of the gas if the container heated to a temperature of 277°C?  
ANS: P2 = 2.93 x 105  
3. A student comes to school by a bicycle whose tire is filled with air at a pressure 240 kPa at 27  
0C. She travels 8 km to reach the school and the temperature of the bicycle tire increases to 39  
0C. What is the change in pressure in the tire when the student reaches school?  
[ANS; 249.6kPa]  
4. An LPG cylinder can withstand a pressure of 14.9 atmosphere. The pressure gauge of the  
cylinder indicates 12 atmosphere at 27°C. Because of a sudden fire in the building, the  
temperature rises. At what temperature will the cylinder explode? [ANS; T=99.50C]  
5. A 30l sample of nitrogen inside a rigid metal container at 200C is placed inside an oven whose  
temperature is 500C. The pressure inside the container at 200C was at 3.00 atm. What is the  
pressure of the nitrogen after its temperature is increased to 500C  
?
[ANS; 3.31atm]  
The General Gas Equation  
•
Any two of the three gas laws can be used to derive the general gas law or equation  
V
∝
T
(Charles’ law) .................  
(Boyle’s law)......................  
(Pressure law) ..................3  
1
P ∝ ퟏ  
2
푽
P
∝
푇