CHARLES’ LAW
Charles’ law states that the volume of a fixed mass of gas at constant pressure is directly proportional to its temperature in the Kelvin scale.
This means that:
When temperature increases, volume increases
When temperature decreases, volume decreases
Mathematically,
V Ξ± T
V = k/T
V = k
T
Hence, V1 = V2
T1 T2
where
(V) = volume of the gas
(T) = absolute temperature (in Kelvin)
The graphical representation of Charles’ law is as shown below:
EXPLANATION OF CHARLES’ LAW USING THE KINETIC THEORY
When a gas is heated, (at constant pressure) its particles gain energy and move faster, pushing the walls of the container outward (to maintain the same number of collisions on the walls of container) so the volume increases. When the gas is cooled, the particles move more slowly and the volume decreases.
Examples
A balloon expands when heated and shrinks when cooled.
Hot air causes a hot-air balloon to rise because the air expands.
Conclusion
Charles’ Law shows how the volume of a gas changes with temperature at constant pressure.
Examples of calculation based on Charles law
A certain mass of a gas occupies 300cm3 at 35oC. At what temperature will it have its volume reduced by half assuming its pressure remains constant?
Solution:
V1 = 300cm3, T1 = 35oC = (35 + 273)K = 308K, V2 = V1/2 = 300/2 = 150cm3, T2 = ?
Using the formula for Charles’ law
V1 = V2
T1 T2
T2 = V2T1 = 150cm3 x 308K = 154K
V1 300cm3
EASY KEMISTRY
CHEMISTRY TEST – CHARLES’ LAW
Time: 30 Minutes
Name: __________________________ Class: __________ Date: __________
Choose the correct option from A–D
1. Charles’ law states that for a fixed mass of gas at constant pressure,
A. volume is inversely proportional to temperature
B. volume is directly proportional to temperature
C. pressure is proportional to temperature
D. pressure is inversely proportional to volume
2. Which of the following must remain constant for Charles’ law to apply?
A. Volume
B. Pressure
C. Temperature
D. Mass and volume
3. The temperature used in Charles’ law calculations must be in
A. degrees Celsius
B. degrees Fahrenheit
C. Kelvin
D. Centigrade
4. If the temperature of a gas is increased, its volume will
A. decrease
B. remains constant
C. increase
D. become zero
5. The mathematical expression for Charles’ law is
A. PV = k
B. V = k
T
C. PV= k
D. V = k
T
6. A gas has a volume of 200 cm³ at 300 K. What will be its volume at 600 K?
A. 100 cm³
B. 200 cm³
C. 300 cm³
D. 400 cm³
7. Which of the following is an application of Charles’ law?
A. Thermometer
B. Hot-air balloon
C. Barometer
D. Syringe
8. When a gas is cooled, its volume
A. increases
B. decreases
C. remains the same
D. doubles
9. A gas occupies 150 cm³ at 300 K. What will be its volume at 600 K?
A. 75 cm³
B. 100 cm³
C. 300 cm³
D. 450 cm³
10. Charles’ law is valid only when
A. pressure is constant
B. volume is constant
C. temperature is constant
D. mass is constant
11. A gas occupies 50 cm³ at 250 K. What will be its volume at 500 K?
A. 25 cm³
B. 50 cm³
C. 75 cm³
D. 100 cm³
12. According to Charles’ law, volume is directly proportional to
A. pressure
B. temperature
C. mass
D. density
13. What happens to the volume of a gas if its temperature is halved?
A. It doubles
B. It halves
C. It remains constant
D. It becomes zero
14. A gas has a volume of 300 cm³ at 300 K. Find its volume at 150 K.
A. 150 cm³
B. 200 cm³
C. 300 cm³
D. 450 cm³
15. The temperature 0°C is equal to
A. 100 K
B. 273 K
C. 373 K
D. 0 K
16. Which of the following instruments shows the effect of Charles’ law?
A. Syringe
B. Thermometer
C. Hot-air balloon
D. Barometer
17. If a gas expands, its temperature must have
A. decreased
B. increased
C. remained constant
D. become zero
18. A gas has a volume of 120 cm³ at 300 K. What will be its volume at 600 K?
A. 60 cm³
B. 120 cm³
C. 180 cm³
D. 240 cm³
19. Charles’ law applies only to
A. solids
B. liquids
C. gases
D. metals
20. When the temperature of a gas is reduced to zero Kelvin, its volume becomes
A. maximum
B. constant
C. minimum
D. zero
THEORY QUESTIONS
1. (a) State Charles’ law.
(b) Define the terms volume and absolute temperature as used in the law.
................................................................................................................................
2. Explain why the volume of a gas increases when it is heated at constant pressure.
3. A gas has a volume of 200 cm³ at 300 K. Calculate its volume at 600 K, assuming the pressure remains constant.
4. (a) Why must temperature be measured in Kelvin when using Charles’ law?
(b) What would happen if Celsius were used instead?
5. State two everyday applications of Charles’ law and explain one of them.
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