Chemistry Class-11: Chapter –6. Thermodynamics Part – 4

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III. Short Answer Type

Question: 20

of water completely vapourises at and bar pressure and the enthalpy change in the process . What will be the enthalpy change for vapourising two moles of water under the same conditions? What is the standard enthalpy of vapourisation for water?


Question: 21

One mole of acetone requires less heat to vapourise than 1 mol of water. Which of the two liquids has higher enthalpy of vapourisation?


Question: 22

Standard molar enthalpy of formation, is just a special case of enthalpy of reaction, . Is the for the following reaction same as ? Give reason for your answer.


No, since has been formed from other compounds and not from its constituent elements.

Question: 23

The value of for is . Calculate enthalpy change for the following reaction:


Question: 24

Enthalpy is an extensive property. In general, if enthalpy of an overall reaction along one route is and ....represent enthalpies of intermediate reactions leading to product B. What will be the relation between for overall reaction and .... etc. for intermediate reactions.



Question: 25

The enthalpy of atomisation for the reaction . What is the bond energy of bond?


Question: 26

Use the following data to calculate for .

for sodium metal

Ionization enthalpy of sodium

Electron gain enthalpy of bromine

Bond dissociation enthalpy of bromine


Question: 27

Given that for mixing of two gases. Explain whether the diffusion of these gases into each other in a closed container is a spontaneous process or not?


It is spontaneous process. Although enthalpy change is zero but randomness or disorder increases. Therefore, in equation , the term will be negative. Hence, will be negative.

Question: 28

Heat has randomising influence on a system and temperature is the measure of average chaotic motion of particles in the system. Write the mathematical relation which relates these three parameters.


Question: 29

Increase in enthalpy of the surroundings is equal to decrease in enthalpy of the system. Will the temperature of system and surroundings be the same when they are in thermal equilibrium?



Question: 30

At for the reaction is . Predict whether the reaction is spontaneous or not.


The reaction is spontaneous