Thermodynamics revision

The diagram shows the variation with volume V of pressure p during one complete cycle of a heat engine.

• A

• B

• A+B

• B-A

In one cycle of a heat engine, 300 J of energy is absorbed and 200 J of energy is ejected. The efficiency of the engine is

• 3/2

• 2/3

• 1/2

• 1/3

The equation of state for an ideal gas, pV = nRT, describes the behavior of real gases

• only at low pressures and large volumes.

• only at high temperatures.

• only at large volumes and large pressures.

• at all pressures and volumes.

When a gas in a thermally insulated cylinder is suddenly compressed, the change of state is

• adiabatic.

• isothermal.

• isobaric.

• isochoric.

The diagram shows the pressure/volume (p/V) diagram for one cycle PQRS of an engine

In which sections of the cycle is work done on the engine?

• SP only

• PQ only

• Sp and PQ only

• RS and SP only

The temperature of an ideal gas is reduced. Which one of the following statements is true

• The molecules collide with the walls of the container less frequently.

• The molecules collide with each other more frequently.

• The time of contact between the molecules and the wall is reduced.

• The time of contact between molecules is increased

The rms velocity of gas molecules is 300 m/s. the rms velocity of molecules of gas with twice the molecular weight and half the absolute temperature is

• 300 m/s

• 150 m/s

• 600 m/s

• 75 m/s

The average kinetic energy of the molecules in an ideal gas is

• directly proportional to the square root of the absolute temperature.

• directly proportional to the absolute temperature.

• independent of the absolute temperature.

• inversely proportional to the absolute temperature.

The requirement that a heat engine must give up some energy at a lower temperature in order to do work corresponds to which law of thermodynamics?

• first

• second

• third

• No law of thermodynamics applies

A gas of mass 16.8 mass is used to fill a 2,93×10^-2m³ balloon at 500K. What is the molar mass of the gas if the pressure is 10⁵ Pa?

• 14 ɡ/mol

• 21 ɡ/mol

• 28 ɡ/mol

• 35 ɡ/mol