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What is Charles's Law (chemistry)?
Grade Level:
Class 8
Space Technology, EVs, Climate Change, Biotechnology, HealthTech, Robotics, Chemistry, Physics
Definition
What is it?
Charles's Law states that for a fixed amount of gas at constant pressure, its volume is directly proportional to its absolute temperature. This means if you increase the temperature of a gas, its volume will also increase, and vice-versa, assuming the pressure doesn't change.
Simple Example
Quick Example
Imagine you have a deflated balloon and you fill it with air inside your home. If you take this balloon out into the hot afternoon sun, you will notice it gets bigger and more inflated. This is because the air inside the balloon heats up, and according to Charles's Law, its volume increases.
Worked Example
Step-by-Step
Let's say a gas in a flexible container has a volume of 2.0 litres at a temperature of 27 degrees Celsius. What will its new volume be if the temperature increases to 127 degrees Celsius, assuming the pressure remains constant?
Step 1: Convert temperatures from Celsius to Kelvin. Add 273 to the Celsius temperature. T1 = 27 + 273 = 300 K. T2 = 127 + 273 = 400 K.
---Step 2: Identify the knowns: V1 = 2.0 L, T1 = 300 K, T2 = 400 K. We need to find V2.
---Step 3: Write down Charles's Law formula: V1/T1 = V2/T2.
---Step 4: Plug in the known values: 2.0 L / 300 K = V2 / 400 K.
---Step 5: Rearrange the formula to solve for V2: V2 = (2.0 L / 300 K) * 400 K.
---Step 6: Calculate V2: V2 = (0.00666...) * 400 = 2.666... L.
---Step 7: Round to a reasonable number of decimal places. V2 = 2.67 L.
Answer: The new volume of the gas will be approximately 2.67 litres.
Why It Matters
Understanding Charles's Law helps engineers design everything from safe airbags in cars to efficient rocket engines for ISRO missions. It's crucial in fields like Space Technology for managing gas temperatures in spacecraft, and in Climate Change studies to understand how atmospheric gases behave. Future scientists and engineers use this law to create better technologies.
Common Mistakes
MISTAKE: Using Celsius temperatures directly in the formula | CORRECTION: Always convert temperatures to Kelvin (absolute temperature scale) before using them in Charles's Law calculations. Kelvin = Celsius + 273.
MISTAKE: Confusing direct proportionality with inverse proportionality | CORRECTION: Charles's Law states volume and temperature are directly proportional, meaning if one increases, the other increases (V/T = constant), unlike Boyle's Law where they are inversely proportional (PV = constant).
MISTAKE: Forgetting to keep pressure constant | CORRECTION: Charles's Law is only valid when the pressure and the amount of gas remain constant. If pressure changes, the law doesn't apply directly.
Practice Questions
Try It Yourself
QUESTION: A balloon contains 10 litres of air at 27 degrees Celsius. If the temperature is raised to 77 degrees Celsius, what will be the new volume of the balloon, assuming constant pressure? | ANSWER: 11.67 litres
QUESTION: A gas occupies 500 mL at 300 K. To what temperature (in Celsius) must it be heated for its volume to double, keeping pressure constant? | ANSWER: 327 degrees Celsius
QUESTION: A gas sample has an initial volume of 3.5 L at 25 degrees Celsius. If its volume is reduced to 2.8 L while maintaining constant pressure, what is the final temperature of the gas in Kelvin? | ANSWER: 238.4 K
MCQ
Quick Quiz
Which of the following statements correctly describes Charles's Law for a fixed amount of gas at constant pressure?
Volume is inversely proportional to temperature.
Volume is directly proportional to temperature.
Pressure is directly proportional to temperature.
Volume is independent of temperature.
The Correct Answer Is:
B
Charles's Law states that for a fixed amount of gas at constant pressure, its volume is directly proportional to its absolute temperature. This means as temperature increases, volume increases.
Real World Connection
In the Real World
You see Charles's Law in action every day! When you cook roti or puri, the dough puffs up because the air and water vapour inside get hot, expand, and increase in volume. Similarly, hot air balloons float because the air inside is heated, expands, becomes less dense, and rises. This principle is also used in designing engines and weather balloons.
Key Vocabulary
Key Terms
VOLUME: The amount of space a substance occupies | TEMPERATURE: A measure of the average kinetic energy of the particles in a substance | PRESSURE: The force exerted per unit area | DIRECTLY PROPORTIONAL: When two quantities increase or decrease together at the same rate | ABSOLUTE TEMPERATURE: Temperature measured on the Kelvin scale, where 0 K is absolute zero.
What's Next
What to Learn Next
Great job understanding Charles's Law! Next, explore Boyle's Law, which explains the relationship between pressure and volume of a gas. Then, you can combine these ideas with the Ideal Gas Law, a powerful concept used in many advanced chemistry and physics applications.
