Test: Thermodynamics Level - 1 - Mechanical Engineering MCQ

Power is measured in Watts.

During free expansion, no work is done by the gas. The gas goes through states of no thermodynamic equilibrium before reaching its final state, which implies that one cannot define thermodynamic parameters as values of the gas as a whole. So work done in a free expansion process is Zero.

An open system is a system that freely exchanges energy and matter with its surroundings.

Perfect gas, also called ideal gas, a gas that conforms, in physical behaviour, to a particular, idealized relation between pressure, volume, and temperature called the general gas law. This law is a generalization containing both Boyle’s law and Charles’s law as special cases and states that for a specified quantity of gas, the product of the volume v and pressure p is proportional to the absolute temperature t; i.e., in equation form, pv = kt, in which k is a constant. Such a relation for a substance is called its equation of state and is sufficient to describe its gross behaviour.

Boyle's Law

a law stating that the pressure of a given mass of an ideal gas is inversely proportional to its volume at a constant temperature.

Charle's Law

a law stating that the volume of an ideal gas at constant pressure is directly proportional to the absolute temperature.

Gay-Lussac's Law

law states that the pressure of a given mass of gas varies directly with the absolute temperature of the gas, when the volume is kept constant.

The average kinetic energy of gas molecules is directly proportional to absolute temperature only; this implies that all molecular motion ceases if the temperature is reduced to absolute zero.

Gay-Lussac's Law

Tlaw states that the pressure of a given mass of gas varies directly with the absolute temperature of the gas, when the volume is kept constant.

Because density of gas and vapour are diferent

Dalton's law (also called Dalton's law of partial pressures) states that in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.

In nonrelativistic classical mechanics, a closed system is a physical system that doesn't exchange any matter with its surroundings, and isn't subject to any net force whose source is external to the system. A closed system in classical mechanics would be considered an isolated system in thermodynamics.

Explanation:
Superheated vapor refers to a state where a substance is heated beyond its boiling point while maintaining its gaseous form. In this state, the vapor does not contain any liquid droplets and is considered to be in a supercritical state.
Here is a detailed explanation of why superheated vapor behaves approximately as a gas:
1. Definition of a gas:
- A gas is a state of matter where particles are widely spread apart and move freely in all directions.
- It does not have a definite shape or volume.
2. Characteristics of superheated vapor:
- Superheated vapor is a gaseous phase of a substance that has been heated above its boiling point.
- It does not contain any liquid droplets.
- The particles in superheated vapor have high kinetic energy and move rapidly.
- The vapor molecules are widely spread apart, similar to a gas.
3. Comparison between superheated vapor and gas:
- Superheated vapor behaves similarly to a gas because both have particles that are widely spread apart and move freely.
- Both superheated vapor and gas do not have a definite shape or volume.
- The behavior of superheated vapor is often approximated to that of a gas due to its similarities in particle movement and distribution.
4. Differences between superheated vapor and steam:
- Steam refers to the gaseous phase of water at or below its boiling point.
- Steam can contain liquid droplets due to condensation or partial vaporization.
- Superheated vapor, on the other hand, does not contain any liquid droplets and is in a more energetic state compared to steam.
In conclusion, superheated vapor behaves approximately as a gas because its particles are widely spread apart, move freely, and do not have a definite shape or volume. However, it is important to note that superheated vapor is a distinct state of matter and should not be confused with steam, which can contain liquid droplets.

PV^γ = constant 

is the expression for Polytropic Process where γ is a constant

If γ = 1, PV = constant which is only true for an isothermal process.

Hence option C is correct.

The specific heats of gases are given as Cp and Cv at constant pressure and constant volume respectively while solids and liquids are having only single value for specific heat.

Avogadro's law states that, "equal volumes of all gases, at the same temperature and pressure, have the same number of molecules." For a given mass of an ideal gas, the volume and amount (moles) of the gas are directly proportional if the temperature and pressure are constant.

Pressure in terms of kinetic energy per unit volume:- The pressure of a gas is equal to two-third of kinetic energy per unit volume of the gas.

P = 2E/3

Kinetic energy of molecules is the form of internal energy in a closed vessel, and internal energy is the function of temperature so kinetic energy of molecules is proportional to absolute temprature

2CO + O₂ = 2 CO₂
(2*28) (16*2) (2*44)

=56 kg =32 kg =88 kg

=1 kg =32/56 kg =88/56 kg

=1 kg =4/7 kg =11/7 kg

That is 4/7 kg of O₂ is required for preaparing 11/7 kg of CO₂ from 1 kg CO.

The absolute zero pressure will be when the molecular momentum of the system becomes zero. ... Thus, Pressure P = F/A = Rate of change of momentum/Area. Now when the ''rate of change of momentum' is zero, the above equation becomes: P = 0 / area = 0 which is the absolute zero pressure.

Liquids are volatile. If taken to zero pressure which effectively means vacuum, in that case, it will boil and vapourise. While different liquids have different viscosity but eventually it will vapourise as there is no pressure to help it maintain the viscosity and surface tension. Water will vapourise much faster than say mercury.

The condition of perfect vacuum, i.e., absolute zero pressure can be attained at. a temperature of - 273.16°C. a temperature of 0°C.

For ordinary calculations - a value of specific heat c_p = 1.0 kJ/kg K (equal to kJ/kg ^oC) or 0.24 Btu(IT)/lb °F - is normally accurate enough

We know by the formula C_p - C_v = R

Avogadro's Law states that equal volumes of all ideal gases (at the same temperature and pressure) contain the same number of molecules.

Boyle's Law states that equal pressure is inversely proportional to volume (when temperature is constant).

Charles's Law states that volume is proportional to temperature (when pressure is constant). Remember that temperature must be measured in Kelvin.

Gay-Lussac's Law states that pressure is proportional to temperature (when volume is constant).

To convert volumetric analysis to gravitational analysis, relative volume of each constituent of flue gases is multiplied by its molecular weight.