What is Gay-Lussac's Law? | Simple Explanation for Class 8

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What is Gay-Lussac's Law (chemistry)?

Grade Level:

Class 8

Space Technology, EVs, Climate Change, Biotechnology, HealthTech, Robotics, Chemistry, Physics

Definition

What is it?

Gay-Lussac's Law states that for a fixed mass of gas kept at a constant volume, its pressure is directly proportional to its absolute temperature. This means if you increase the temperature, the pressure of the gas also increases, and vice-versa.

Simple Example

Quick Example

Imagine you are making chai in a pressure cooker. When you heat the cooker (increase temperature), the steam inside builds up pressure. If the pressure gets too high, the whistle blows to release it. This shows how increasing temperature directly increases the pressure inside the fixed volume of the cooker.

Worked Example

Step-by-Step

A gas in a sealed container has a pressure of 200 kPa at a temperature of 27°C. If the temperature is raised to 127°C, what will be the new pressure?

Step 1: Convert temperatures to Kelvin. Remember, K = °C + 273.
T1 = 27°C + 273 = 300 K
T2 = 127°C + 273 = 400 K
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Step 2: Write down the given pressure.
P1 = 200 kPa
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Step 3: Apply Gay-Lussac's Law formula: P1/T1 = P2/T2.
200 kPa / 300 K = P2 / 400 K
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Step 4: Solve for P2.
P2 = (200 kPa / 300 K) * 400 K
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Step 5: Calculate the value.
P2 = (2/3) * 400 kPa
P2 = 800/3 kPa
P2 = 266.67 kPa

Answer: The new pressure will be approximately 266.67 kPa.

Why It Matters

This law is crucial for designing engines in EVs, understanding rocket propulsion in Space Technology, and even predicting weather patterns. Engineers use it to build safe pressure vessels and scientists apply it in fields like Climate Change to study atmospheric gases.

Common Mistakes

MISTAKE: Using Celsius or Fahrenheit directly in calculations | CORRECTION: Always convert temperature to the absolute Kelvin scale (K = °C + 273) before using it in the formula.

MISTAKE: Assuming an inverse relationship between pressure and temperature | CORRECTION: Remember, pressure and absolute temperature are directly proportional; if one increases, the other increases, given constant volume.

MISTAKE: Forgetting that the volume of the gas must remain constant for the law to apply | CORRECTION: Always check if the problem states a 'sealed container' or 'constant volume' to confirm Gay-Lussac's Law is applicable.

Practice Questions

Try It Yourself

QUESTION: A gas in a rigid container has a pressure of 150 kPa at 300 K. What will be its pressure if the temperature is increased to 450 K? | ANSWER: 225 kPa

QUESTION: The pressure inside a gas cylinder is 3 atm at 27°C. If the cylinder is accidentally heated to 77°C, what will be the new pressure inside? (Assume constant volume) | ANSWER: 3.5 atm

QUESTION: A sealed aerosol can has a pressure of 2.5 atm at 20°C. If the maximum safe pressure for the can is 4 atm, what is the highest temperature (in °C) it can withstand before becoming dangerous? | ANSWER: 204.8°C

MCQ

Quick Quiz

Which of the following conditions must be constant for Gay-Lussac's Law to be valid?

Pressure and Temperature

Volume and Number of moles of gas

Temperature and Number of moles of gas

Pressure and Number of moles of gas

The Correct Answer Is:

Gay-Lussac's Law describes the relationship between pressure and temperature when the volume and the amount (number of moles) of gas are kept constant.

Real World Connection

In the Real World

This law is used by engineers at ISRO when designing fuel tanks for rockets. The gases inside these tanks experience extreme temperature changes, and understanding Gay-Lussac's Law helps ensure the tanks can safely handle the resulting pressure variations without bursting. It's also vital in designing safe LPG cylinders used in every Indian home.

Key Vocabulary

Key Terms

Pressure: The force exerted by gas particles on the walls of their container. | Temperature: A measure of the average kinetic energy of the gas particles. | Absolute Temperature: Temperature measured on the Kelvin scale, where 0 K is absolute zero. | Constant Volume: The container holding the gas does not change its size. | Proportional: Two quantities change at the same rate; if one doubles, the other doubles.

What's Next

What to Learn Next

Next, you should learn about Charles's Law and Boyle's Law. These laws, along with Gay-Lussac's Law, are the foundational gas laws that help us understand how gases behave under different conditions, and they all combine into the Ideal Gas Law!