MCQs on First Law of Thermodynamics and Hess Law

The first law of thermodynamics is the law of conservation of energy, that is energy cannot be created or destroyed but is converted from one form to another. Expressed in an alternative way the first law of thermodynamics states that the total energy of the universe is constant. When a certain property of a system is independent of how that system attains the state that exhibits such a property the property is deemed to be a state function. Hess’s law states that a reaction enthalpy is the sum of the enthalpies of any path into which the reaction may be divided at the same temperature and pressure. The change in enthalpy is independent of the path followed. For this reason enthalpy like internal energy is also a state function, a quantity whose value is determined only by the state of the system in question.

1. The variations in enthalpy that can not be detected per calorimeter can be detected with the aid of

  1. Newton’s law
  2. Hess’s law
  3. Krebs law
  4. Ohm’s law

Answer: (b)

2. The energy required to sever a given covalent bond is named

  1. bond energy
  2. bond enthalpy
  3. bond dissociation energy
  4. all of above

Answer: (d)

3. Changes in enthalpy in an exothermic reaction is

  1. positive
  2. negative
  3. constant
  4. neutral

Answer: (b)

4. The first law of thermodynamics states that energy can not be

  1. created only
  2. destroyed only
  3. converted
  4. created and destroyed

Answer: (d)

5. Hess’s law states that a chemical reaction is independent of the route by which chemical reactions takes place while keeping the same

  1. initial conditions only
  2. final conditions only
  3. mid-conditions
  4. initial and final conditions

Answer: (d)

6. The standard enthalpy change of neutralization involves the reaction of an acid with an alkali to form 1 mol of

  1. water
  2. oxygen
  3. nitrogen
  4. anhydrous salt

Answer: (a)

7. The change in the energy between a chemical reaction and the surroundings at constant temperature is called

  1. enthalpy change
  2. enthalpy
  3. enthalpy profile
  4. dynamic enthalpy

Answer: (a)

8. To initiate a reaction the minimum energy which is required to break bonds is called

  1. bond energy
  2. activation energy
  3. breaking energy
  4. ionization energy

Answer: (a)

9. The standard condition for enthalpy changes are

  1. the pressure of 100 kPa
  2. temperature 298K
  3. normal physical state
  4. all of above

Answer: (d)

10. The application of law of thermodynamics to the enthalpy change was done by

  1. Newton
  2. Hess’s
  3. Lewis
  4. Sophocles

Answer: (b)

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