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What is the Combined Gas Law (gas law)?
Grade Level:
Class 6
Space Technology, EVs, Climate Change, Biotechnology, HealthTech, Robotics, Chemistry, Physics
Definition
What is it?
The Combined Gas Law helps us understand how the pressure, volume, and temperature of a fixed amount of gas are all related. It combines three simpler gas laws (Boyle's Law, Charles's Law, and Gay-Lussac's Law) into one useful equation. This law tells us that if any of these three factors change, the others will also change in a predictable way.
Simple Example
Quick Example
Imagine you have a bicycle tyre. If you pump more air (gas) into it, the pressure inside increases, and the volume of the tyre also expands slightly. If the day gets hotter, the air inside the tyre heats up, and its pressure increases even more, which is why tyres can sometimes burst in summer if over-inflated.
Worked Example
Step-by-Step
Let's say a gas in a cylinder has an initial pressure of 2 atm, a volume of 5 litres, and a temperature of 300 Kelvin. If the pressure changes to 4 atm and the temperature changes to 400 Kelvin, what will be the new volume?
Step 1: Write down the formula for the Combined Gas Law: (P1 * V1) / T1 = (P2 * V2) / T2
---Step 2: List the given values:
P1 = 2 atm
V1 = 5 litres
T1 = 300 K
P2 = 4 atm
T2 = 400 K
V2 = ?
---Step 3: Plug the values into the formula:
(2 * 5) / 300 = (4 * V2) / 400
---Step 4: Simplify the left side:
10 / 300 = (4 * V2) / 400
0.0333 = (4 * V2) / 400
---Step 5: Isolate V2 by multiplying both sides by 400:
0.0333 * 400 = 4 * V2
13.32 = 4 * V2
---Step 6: Divide by 4 to find V2:
V2 = 13.32 / 4
V2 = 3.33 litres
---Answer: The new volume of the gas will be 3.33 litres.
Why It Matters
Understanding the Combined Gas Law is crucial for engineers designing rockets for ISRO, predicting weather patterns, and even for doctors using medical gas cylinders. This concept helps professionals in Space Technology, HealthTech, and Climate Change make important calculations and decisions, ensuring safety and efficiency in their work.
Common Mistakes
MISTAKE: Using Celsius or Fahrenheit for temperature in calculations. | CORRECTION: Always convert temperature to Kelvin (K) before using it in the Combined Gas Law formula. Kelvin = Celsius + 273.15.
MISTAKE: Mixing up which variables are initial (1) and final (2). | CORRECTION: Clearly label all your initial values as P1, V1, T1 and final values as P2, V2, T2 to avoid confusion.
MISTAKE: Not keeping units consistent (e.g., using litres for one volume and millilitres for another). | CORRECTION: Ensure all pressure units are the same (e.g., both atm or both Pa), and all volume units are the same (e.g., both litres or both m^3) throughout the calculation.
Practice Questions
Try It Yourself
QUESTION: A gas has a pressure of 1 atm, a volume of 10 litres, and a temperature of 250 K. If its pressure increases to 2 atm and volume decreases to 6 litres, what is the new temperature? | ANSWER: 300 K
QUESTION: A balloon contains 5 litres of air at 27 degrees Celsius and 1.5 atm pressure. If the balloon is moved to a place where the temperature is 77 degrees Celsius and the pressure is 2 atm, what will be its new volume? (Remember to convert Celsius to Kelvin first!) | ANSWER: 4.1 litres
QUESTION: A gas in a container has a volume of 200 ml at 0 degrees Celsius and 760 mmHg pressure. If its volume is reduced to 150 ml and the temperature is raised to 50 degrees Celsius, what is the new pressure in mmHg? | ANSWER: 1205.5 mmHg
MCQ
Quick Quiz
Which of these factors must always be converted to Kelvin when using the Combined Gas Law?
Pressure
Volume
Temperature
All of the above
The Correct Answer Is:
C
Temperature must always be in Kelvin (K) for gas law calculations because the Kelvin scale is an absolute temperature scale, unlike Celsius or Fahrenheit, which have zero points that do not represent the absence of thermal energy.
Real World Connection
In the Real World
The Combined Gas Law is used by meteorologists in India to understand how atmospheric pressure, temperature, and volume of air masses change, which helps them predict weather patterns like monsoons or heatwaves. It's also vital for scuba divers who need to calculate how the volume of air in their tanks changes with pressure and temperature as they dive deeper into the ocean.
Key Vocabulary
Key Terms
PRESSURE: The force exerted by gas particles on the walls of their container. | VOLUME: The amount of space a gas occupies. | TEMPERATURE: A measure of the average kinetic energy of gas particles, indicating how hot or cold something is. | KELVIN: The absolute temperature scale used in gas law calculations, where 0 K is absolute zero.
What's Next
What to Learn Next
Great job understanding the Combined Gas Law! Now that you know how pressure, volume, and temperature are connected, you're ready to explore the 'Ideal Gas Law'. This next concept adds the 'amount of gas' into the equation, helping you understand even more complex real-world gas situations. Keep up the amazing work!
