**Question (11) : State Laws of conservation of energy?**

**Answer :**According to the laws of conservation of energy, “energy can neither be created nor be destroyed. It can only be transformed from one form to another.”

**Question (12) : Is the boiler a closed system?**

**Answer :**Yes definitely the boiler is a closed system.

**Question (13) : What is the importance of the Thermodynamics in the field of Mechanical Engineering?**

**Answer :-**All the mechanical engineering systems are studied with the help of thermodynamics. Hence it is very important for the mechanical engineers.

**Question (14) : Which formula forms a link between the Thermodynamics and Electro chemistry?**

**Answer :**Gibbs Helmholtz formula is the formula which forms the link between the thermodynamics and electromagnetism.

ΔHs/R = [∂ lnp /∂ (1/T)]x

where: x – mole fraction of CO2 in the liquid phase

p – CO2 partial pressure (kPa)

T – temperature (K)

R – universal gas constant

α – mole ratio in the liquid phase (mole CO2 per mole of amine)

**Question (15) : Which is the hardest compound known?**

**Answer :**Diamond.

**Question (16) : Which has more efficiency: Diesel engine or Petrol engines?**

**Answer :**Off course Diesel engine has the better efficiency out of two.

**Question (17) : How many Laws of Thermodynamics are there?**

**Answer :**There are four laws of the thermodynamics.

**Zeroth law of thermodynamics:**If two systems are in thermal equilibrium with a third system, they must be in thermal equilibrium with each other. This law helps define the notion of temperature.

**First law of thermodynamics:**Because energy is conserved, the internal energy of a system changes as heat flows in or out of it. Equivalently, machines that violate the first law (perpetual motion machines) are impossible. Heat is the flow of thermal energy from one object to another.

**Second law of thermodynamics:**The entropy of any isolated system cannot decrease. Such systems spontaneously evolve towards thermodynamic equilibrium — the state of maximum entropy of the system. Equivalently, machines that violate the second law (perpetual motion machines) are impossible.

**Third law of thermodynamics:**The entropy of any pure substance in thermodynamic equilibrium approaches zero as the temperature approaches zero. The entropy of a system at absolute zero is typically zero, and in all cases is determined only by the number of different ground states it has.

**Question (19) : What is the difference between Critical Speed and Whirling Speed?**

**Answer :-**In Solid mechanics, in the field of rotor dynamics, the critical speed is the theoretical angular velocity which excites the natural frequency of a rotating object, such as a shaft, propeller or gear. As the speed of rotation approaches the objects natural frequency, the object begins to resonate which dramatically increases system vibration. The resulting resonance occurs regardless of orientation.Whirling Speed is due to the unbalanced forces acting on a rotating shaft.

**Question (20) : What is Hess Law?**

**Answer :**According to the Hess law the energy transfer is simply independent of the path being followed. If the reactant and the product of the whole process are the same then same amount of energy will be dissipated or absorbed.

**Question (21) : Explain Second Law of Thermodynamics?**

**Answer :-**The entropy of the universe increases over time and moves towards a maximum value.

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