3.Which assumption of kinetic molecular theory breaks down under conditions of h

Question

3.Which assumption of kinetic molecular theory breaks down under conditions of high pressure? (a) The size of the gas particle is negligibly small. (b) The average kinetic energy of the gas particle is proportional to the temperature in Kelvins (c) The collision of one gas particle with another (or with the walls of the container) is completely elastic. 4. You buy a cup of coffee at The Sip and while doing homework, it cools to room temperature and reaches thermal equilibrium with its surroundings. If the cup is the system, identify the energy exchange as primarily heat or work and determine whether the sign of AE is positive or negative for the SYSTEM.

Explanation / Answer

Ans. #3. The assumption “size of the gas particles is negligibly small” indicates the volume occupied by gas particles (say, all the gas particles are clumped together by freezing) is negligible compared to the volume of the container.

# For example 1 mol of H2 (= 2.0 g, say 2.0 mL when hypothetically frozen) occupies a volume of 22.4 L (= 22400 mL) at STP. So, the volume occupies by gas particles (around 2.0 mL, hypothetically) is negligible compared to 22400.0 mL of the container.

            (Container / gas particle) volume ration = 22400 / 2 = 11200

# However, when the pressure is increased, say, the same conditions as above but at 50 atm pressure, the volume of container shall be around 0.4485 L = 448.5 mL.

            (Container / gas particle) volume ration = 448 / 2 = 224

Compare the two ratios, the volume of gas particles can’t be taken negligible compared to the volume of container at high pressure.

# Therefore, at high pressure, the assumption “size of the gas particles is negligibly small” does not hold true.

# So, correct option is – a. size of the gas particles is negligibly small

#4. Energy is exchanged in form of HEAT.

The sign of dE is NEGATIVE. The loss of heat from the system (cup) is denoted by –ve sign.

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