First Law of Thermodynamics and Hess Law MCQs

The first law of thermodynamics, also known as the law of conservation of energy, asserts that energy cannot be created or destroyed, only converted from one form to another. Alternatively, it can be expressed as the total energy of the universe remaining constant. A property of a system that remains constant regardless of the method used to achieve that state is referred to as a state function. Hess’s law states that the enthalpy change of a reaction is the sum of the enthalpies for any series of steps that lead to the reaction, provided the temperature and pressure remain constant. Thus, enthalpy, like internal energy, is a state function because its value depends solely on the state of the system, not on the path taken to reach that state.

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

(a) Newton’s law
(b) Hess’s law
(c) Krebs law
(d) Ohm’s law

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

(a) enthalpy change
(b) enthalpy
(c) enthalpy profile
(d) dynamic enthalpy

Changes in enthalpy in an exothermic reaction is

(a) positive
(b) negative
(c) constant
(d) neutral

The energy required to sever a given covalent bond is named

(a) bond energy
(b) bond enthalpy
(c) bond dissociation energy
(d) all of above

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

(a) water
(b) oxygen
(c) nitrogen
(d) anhydrous salt

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

(a) Newton
(b) Hess’s
(c) Lewis
(d) Sophocles

The standard condition for enthalpy changes are

(a) the pressure of 100 kPa
(b) temperature 298K
(c) normal physical state
(d) all of above

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

(a) initial conditions only
(b) final conditions only
(c) mid-conditions
(d) initial and final conditions

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

(a) bond energy
(b) activation energy
(c) breaking energy
(d) ionization energy

The first law of thermodynamics states that energy can not be

(a) created only
(b) destroyed only
(c) converted
(d) created and destroyed