BOYLE’S LAW.
1. State Boyle’s Law
The pressure of a fixed mass of a gas is inversely proportional to its
volume at a constant temperature.
2.
... [Show More] State how the pressure of a fixed mass of gas can be increased at constant
temperature. (1mk)
When the volume is decreased (the gas is compressed), the spacing
between the molecules is decreased, and therefore the rate at which they
collide with the walls of the container is increased – so the pressure
increases.
3. An air bubble expands as it rises to the surface of water in a deep pond. State
the cause of this given that the temperature remains constant. (1mk)
Decrease in pressure due to water as the bubbles rises to the top it
expand since pressure increases with depth.
4. When an inflated balloon is placed in a refrigerator, it is noted that its volume
reduces. Use kinetic theory to explain this observation. (1mk)
Low temperature reduces the kinetic energy of molecules which lead to
lower rate of collision which results to reduction of pressure.
5. Show that the density of a fixed mass of gas is directly proportional to the
pressure at constant temperature.
Ideal gas Equation is given in the form PV=ηRT……(i)
Where moles of the gas (η) =
Using η=
and rearranging equation (i) yields
=
But
= ρ (Density)
Then, ρ=
…………….(ii)
Equation (ii) implies that ρ is directly proportional to p at constant T since M
and R are constants.
6. Draw axes and sketch the P – V graph for a gas obeying Boyle’s Law.
Mass and temperature
CHARLE’S LAW.
1. State Charles law for an ideal gas. (1mk)
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The volume of a fixed mass of a gas is directly proportional to the absolute
temperature(Kelvin) at constant pressure.
2. When an inflated balloon is placed in a refrigerator it is noted that its volume
reduces.
Low temperature reduces the kinetic energy of molecules, and therefore the rate
at which they collide with the walls of the container is reduces which results to
reduction of volume.
3. Define absolute zero temperature for an ideal gas (1mk)
Absolute zero temperature refers to the lowest temperature a gas can fall
to. It is -2730
celcius (0 Kelvin).
4. The pressure of the air inside a car tyre increases if the car stands out in the sun
for some time on a hot day. Explain the pressure increase in terms of the kinetic
theory of gases. (3mk)
When the temperature of the air inside the tyre increase the kinetic energy of air
particles increases and therefore the rate at which they collide with the walls of
the tyre is increased – so the pressure increases.
5. Using the kinetic theory of gases, explain the behaviour of gas particles in
accordance with Charles Law. (2mk)
When the temperature of a gas rises, its particles move faster and exert a
larger force on the wall of the container when they collide with it.
The frequency of collisions also increases.
If the pressure is to remain constant, the volume must increases.
OR
When a gas is heated the kinetic energy of its molecules increases.
If the volume remains constant the pressure at the walls would increase
due to a greater rate of change of momentum per unit time.
Since Charles law is done at constant pressure, and then the volume
increases.
6. You are provided with the following
A uniform glass tube
An index of sulphuric acid
A thermometer
A stirrer
A meter scale (Ruler)
Water bath and a source of heat
Using a suitable diagram, explain how the above may be used to verify Charles’
law
PRESSURE LAW.
1. State the pressure law for an ideal gas (1mk)
The pressure of a fixed mass of a gas is directly proportional to the absolute
temperature(Kelvin) at a constant volume.
2. A gas is enclosed in a glass container and the container is heated. Explain why
the pressure of the gas increases. (1mk)
Raising the temperature increases the average speed of particles so they
collide more vigorously and more frequently with container walls. If the
volume does not increase the pressure must rise.
3. Explain why gas cylinders are likely to expand incase of a fire out break(2mk)
When a gas is heated, Temperature of a gas rises, its particles move faster and
exert a larger force on the wall of the cylinder.
If the pressure remain constant, the volume must increase thus expand.
4. Using Kinetic theory of Gases, explain how the rise in temperature of a gas
causes rise in the pressure of a gas if the volume is kept constant.(3mk)
Raising the temperature increases the average speed of particles so they
collide more vigorously and more frequently with container walls.
If the volume does not increase, pressure increases.
5. A house in which a cylinder containing cooking gas is kept unfortunately catches
fire. The cylinder explodes. Give a reason for the explosion.
From pressure law, when a gas is heated due to fire Temperature
increases which led to increase in pressure at constant volume, when
pressure increases it can led to explosion.
6. Define the absolute zero temperature (1mk)
Absolute zero temperature refers to the lowest temperature a gas can fall
to. It is -2730
celcius (0 Kelvin).
7. The diagram below shows a set up that a student used to investigate the
pressure law [Show Less]