With reference to the action of Carbon Dioxide (CO2) extinguishers, consider the following statements: 1. When released from a cylinder, CO2 contracts in volume and heats up. 2. The expansion of CO2 cools down the temperature of the fuel. 3. Dry powder of chemicals like sodium bicarbonate can be used to release CO2 near a fire. Which of the statements given above are correct?

Correct Option The correct option is (c). Explanation Carbon dioxide ($CO_2$) is a common fire extinguishing agent used for electrical fires and inflammable liquids. It functions primarily by displacing oxygen (blanketing effect) and secondarily by cooling the fuel. Certain chemical powders also release $CO_2$ upon thermal decomposition to achieve a similar effect. Statement-wise Analysis - Statement 1 is Incorrect. $CO_2$ is stored in cylinders under high pressure (often in liquid form). When released, it expands enormously in volume, not contracts. According to the principles of thermodynamics (adiabatic expansion), the rapid expansion of a gas results in a significant drop in temperature, not heating. - Statement 2 is Correct. Due to the rapid expansion described above, the $CO_2$ gas cools down drastically as it exits the nozzle. This cooling effect helps lower the temperature of the burning fuel and the surrounding area, aiding in extinguishing the fire. - Statement 3 is Correct. Sodium bicarbonate ($NaHCO_3$) is commonly used in dry chemical fire extinguishers. When this powder is sprayed near a fire, the heat causes it to decompose ($2NaHCO_3 \rightarrow Na_2CO_3 + H_2O + CO_2$). This reaction releases carbon dioxide, which helps smother the fire by cutting off the oxygen supply. Key Takeaway $CO_2$ Extinguishers: Work by cutting off the oxygen supply (being heavier than air) and cooling the fuel (due to expansion). Sodium Bicarbonate: Decomposes under heat to release $CO_2$, making it an effective dry chemical extinguishing agent.

With reference to the action of Carbon… - NCERT Class 8 Science MCQ

NCERT Class 8 Science — Chapter 2: Combustion and flame

mcqmedium

With reference to the action of Carbon Dioxide (CO2) extinguishers, consider the following statements:

When released from a cylinder, CO2 contracts in volume and heats up.
The expansion of CO2 cools down the temperature of the fuel.
Dry powder of chemicals like sodium bicarbonate can be used to release CO2 near a fire.

Which of the statements given above are correct?

NCERT textbook question

From NCERT Science - class 8 · Page 6

Options

A1 and 2 only
B2 only
C2 and 3 only
D1, 2 and 3

Did you get this right?

Solution

Correct Option

The correct option is (c).

Explanation

Carbon dioxide ($CO_2$) is a common fire extinguishing agent used for electrical fires and inflammable liquids. It functions primarily by displacing oxygen (blanketing effect) and secondarily by cooling the fuel. Certain chemical powders also release $CO_2$ upon thermal decomposition to achieve a similar effect.

Statement-wise Analysis

Statement 1 is Incorrect. $CO_2$ is stored in cylinders under high pressure (often in liquid form). When released, it expands enormously in volume, not contracts. According to the principles of thermodynamics (adiabatic expansion), the rapid expansion of a gas results in a significant drop in temperature, not heating.
Statement 2 is Correct. Due to the rapid expansion described above, the $CO_2$ gas cools down drastically as it exits the nozzle. This cooling effect helps lower the temperature of the burning fuel and the surrounding area, aiding in extinguishing the fire.
Statement 3 is Correct. Sodium bicarbonate ($NaHCO_3$) is commonly used in dry chemical fire extinguishers. When this powder is sprayed near a fire, the heat causes it to decompose ($2NaHCO_3 \rightarrow Na_2CO_3 + H_2O + CO_2$). This reaction releases carbon dioxide, which helps smother the fire by cutting off the oxygen supply.

Key Takeaway

$CO_2$ Extinguishers: Work by cutting off the oxygen supply (being heavier than air) and cooling the fuel (due to expansion).
Sodium Bicarbonate: Decomposes under heat to release $CO_2$, making it an effective dry chemical extinguishing agent.

Your note

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