Thermochemistry

Question 7.1: Define the following terms and give three examples of each. (i) system (ii) surrounding (iii) state function
Answer.
System: Anything (material) under test in the laboratory. or Any portion of universe which is under study is called system. Examples: Reaction between Zn andCuSO4 solution. (ii) One mole of oxygen enclosed in a cylinder fitted with piston (iii) Neutralization reaction of HCl and NaOH.
Surrounding: All the material of universe which surrounds the system but do not form a part of system. Examples: Consider the reaction between Zn and CuSO4 which is taking place in a cylinder lying on the table and air is surrounding it. If the reaction is our system then cylinder, table and air are surroundings.
State function: The macroscopic property of system whose value depends only on the current state of the system is called state function. The amount of change in a state function depends only on the initial and final states, not on the path adopted to bring about change. Example: Pressure (P), temperature (T), Volume (V), internal energy (E), are all state functions of a system.
Question 7.2: Differentiate between the following:
Internal energy and Enthalpy
Answer
Enthalpy: Total heat content of the system is called enthalpy. It is denoted by H. Generally enthalpy of a system is equal to internal energy plus the product of pressure and volume of the system. It is not practicable to find the absolute value of enthalpy of the system, but enthalpy change (∆H) can be measured experimentally. H = E + PV
Internal Energy. Total of all possible kinds of energies of the system is called internal energy. It is denoted by E. Generally internal energy is sum of kinetic energy and potential energies of the particles in the system. Kinetic energy is due to the translational, rotational, vibrational movement of the particles and potential energy is due to attractive forces (within molecules and between molecule).

Enthalpy change and internal energy change
Answer
Enthalpy change: Amount of heat evolved or absorbed in a reaction at constant pressure is called enthalpy change. It is denoted by ∆H.
Internal energy change: Amount of heat evolved or absorbed in a reaction at constant volume is called internal energy change. It is denoted by ∆E.
Exothermic reaction and Endothermic reaction:
Answer
Exothermic reaction: The reaction which releases heat to the its surroundings is called exothermic reaction. OR The reaction in which enthalpy of product is less than the enthalpy of reactant is called exothermic reaction.
Endothermic reaction: The reaction which absorbs heat from its surroundings is called exothermic reaction. OR The reaction in which enthalpy of product is greater than enthalpy of reactant is called endothermic reaction.

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Chemistry

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